Enlighten one :)

I have to say my first response was compassion and trust, but as I returned for follow up messages and responses. There are red flags all over his post. Beginning with the fact that his post was 5 am. Now because I do not know if that is my time, his time or visa journey’s time I did not draw attention to this. He stated he was in a shelter that I am assuming does not have internet access at that time of the morning.
His note was very detailed, but at the same time awfully vague. Reading his first post again, it seems like he was in Maine. In his 2nd post he is someplace that he didn't even mention in his first post. His responses to our questions were vague and indirect, which just leads me to believe that this story is false.
Since I am chief fraud police and informant, I must render my determination that this post has con and fake spelled out all over.

Unfortunately, when we engage in a long distance relationship we never really know how our spouse really behaves in every day situations.
Your Husband seems like he is acting out of insecurity. He is not secure in who he is so he puts you down. This is nothing you can change if he does not acknowledge his own self doubt.
You can give him all the confidence and reassurance, but it will never be enough for him to validate himself. He sounds controlling. If he controls you, it gives him validation. If you step outside of that control he looses control.
I recomend you seek counciling as a couple if you want to save the relationship. Just in yoru short post he does not seem like someone who will volunteer to go though.
I wish you well and piece. Remember it is not what youare doing that makes him react this way. It is how he feels inside.

Only she can stop the drinking. You can't want it enough for her.
She has to want it for herself.
Your GC is fine considering you were married 6 years.

The why, where, & how are irrelevant at this point. You need to focus on you from this point forward. If it was not him, it would have been someone else for something different just as unhealthy or healthy. You need to grow and learn from this experience. Do not think about what you could have done differently. Think about what you can do differently for yourself emotionally & spiritually to be stronger and prevent yourself from being in another unhealthy relationship. We are only as healthy as the people we keep in our lives.
Accept your experience as a blessing and opportunity on to bigger and better things. You are one amazing women to endure this process. Just think of other things you can accomplish and overcome now that you have been through this journey.

My thoughts and prayers are with you and your baby. I know the God we serve has already won this victory for you. It's just the battle that makes us weary but you can and WILL pull through. You will emerge even stronger and even wiser. Vengeance is mine saith the Lord! It's wonderful that He vindicates just for us! Even in your storm praise Him anyhow...and watch the reward.

The problem with the greencard being involved is it's such an urgent decision.. you don't have the proper time to process so you have 2 "worst case" scenario's bouncing around in your head:
1. You either stick with it and possibly end up supporting your ex-husband (and possibly his girlfriend by association) in his new life in America, OR
2. You end up wishing you hadn't let him go back to his country and wishing you had given it a shot
Of the two worst case scenario's, which one scares you the most? For me, scenario 2 is actually something I could live with... the reason being I didn't break the relationship, I didn't cheat. I gave my all to the relationship just to be slapped in the face (not literally). I think I would be upset, and hurt quite a bit because it's understandable that you don't just "fall out of love" with someone because they cheated but without trust what sort of relationship can you really have?. Scenario 1 I can see myself becoming bitter if I am supporting my ex and his new "flings". I can see myself angry and stressed out that I can't just "forget" about him or at least push him to the back of my mind. I would need to mention to any new partner/husband that I am supporting my ex who immigrated and I can't say I wouldn't be a little embarrassed feeling people might judge me and automatically assume I was scammed.
Also, with the I-864 being binding once AOS is complete, if you ever want to petition another person from overseas you would need to declare the current I-864 in the "household" count making your financial requirements higher. Not saying you WILL, just as an example to others.
I think perhaps we should take the GC out of the equation and instead focus on the relationship. If the greencard wasn't an issue and he was American, would you stay with him? Honestly? If you hadn't put all this work into the visa stuff, and if instead you had spent the last months waiting, actually together.. would it make it harder to say goodbye? Or easier? What is it about him that makes you want to forgive him? Forget the "love" part of it... many fools are made because of love.. think rationally, what is it you would miss about him? Would what you miss be overridden by the knowledge that he cheated? Would you ALWAYS think back to that? He's trying to confuse you.. I think he should go and stay with friends or in a motel or something for a while so you can think about things. Don't do any action on the file, postpone the biometrics by sending in the letter and putting a date on the letter say, a month away from the date that's booked now.. make the process stall (he's still not deportable while waiting for the GC answer) so you have time to think.
Cheating is a BIG no-no for me. My main issues being (and please I don't mean to upset you) your husband had to consciously put you out of his mind. He KNEW he had a visa petition in the works, it's not like it's a normal "separation".. this working behind the scenes, you know someone's thinking about you and wishing and hoping you were with them. Plus all the time you talked to him online there were a couple of times where he may have just got back from his latest love interest. Or a time he wasn't online or couldn't call because he was with someone else. It would eat me up inside wondering.. and it doesn't seem like he wants to fix things by being honest about it... and even if he SAID he was being honest I don't know if I could believe that.. or get the images out of my head... There are SO many times during "cheating" that he consciously stopped thinking about you. Your feelings were irrelevant to him at that moment... or those moments. He saw another woman naked and HAD to have thought of you or stopped himself from doing so. If he didn't have to stop himself from thinking of you he doesn't love you. I know I think about my husband all the time. If I'm in a store and I see something he likes, or I wonder how work is, or just randomly around the house while thinking about what's for dinner. When we were apart I was thinking basically the same thing and always wishing when I hopped into bed at night wishing that my guy was with me. I just couldn't handle knowing that he doesn't love me like I love him, and that our values weren't the same... on something SO important as being faithful.
*Edit - Most importantly (I just re-read your OP), your guy didn't just CHEAT on you, he fell in love with another woman. Another woman that is in the US. Another woman that he emailed saying he can't wait to get there and leave YOU for... but you found out. I know you don't want to think you've been scammed because yes, people DO cheat all the time but that IS a type of scamming. He wasn't necessarily scamming you for the GC but he did use you to get to his REAL love interest and now he's saying pretty words to confuse you enough to get the greencard.. including telling you he'd go home... and he might but honestly then I think he'd have this real love interest petition for him anyway. His options are get the greencard through you, or go home to await his real love... the former being the quickest option. He might have loved you in the beginning and rather than restarting the visa with his real love, and spending more money on it, he decided that it was just easier to carry on and get it through you.
I think the risks are far too great that you're being scammed. I couldn't bear knowing I'd been made a fool of... and I REALLY don't think he'll stop cheating... he might not TELL you, it might take you months to find out.. but leopards don't change their spots.

Whether he was an American...Nigerian or from London ...she got SCAMMED. He is not who he presented to be.
I guess what you do not understand Nwanyioma is that it is easier to say the relationship just did not work out then to say you got scammed. I tried to pretend my relationship didn't work out at first. I wanted to follow through on helping him stay here so I could be the nice person. It was soo much easier, but then he called the cops on me when I was not home. Oh no I was not going to get away that easy.
So that is bullshit when you say use the "I got scammed card"
You have no idea those feelings until you start reading the letter and emails that show this man is not who he represented. Whether it was for money, love, sex, or the American dream...it is called a scamming when someone behaves a certain way to get a certain thing.

While it is possible for a divorced immigrant to get the conditions of his residence removed and to receive an unrestricted, 10-year Green Card with a waiver, I do understand your concern regarding the age difference.
The general assumption is that age doesn't matter when it comes to love and partnership, yet it might carry some weight when it comes to a woman in her Fifties who married an immigrant in his Twenties and the marriage failed prematurely. This rather large age gap might not be a formal factor for the Immigration Officer when trying to judge whether it's a bona fide marriage or not, but it might be an underlying and influential factor nonetheless when figuring out whether or not to approve the applicant's petition.
Is it fair to even bring age into the equation? I don't really know, in most cases probably not. Generally speaking, people of different ages might very well be madly in love and live together in harmony until death takes them apart. Yet in real life, every case is different and has unique factors to consider, so in your husband's case it's important that he can firmly establish that your marriage was entered in good faith, and not in order to gain immigration benefits.
Playing devil's advocate, assuming an Immigration Officer is suspicious of fraudulent activity between the US citizen and the immigrant. Would you think that if one party, the US citizen, wrote a letter stating that their marriage was real, would carry much weight? What would carry more weight is an affidavit from a person outside your relationship, someone who can attest that he or she has experienced both of you as a loving couple.