Aline SC

Hi,
 
A couple of things.
 
First the 6 month visit is NOT guaranteed. The border officer decides how long you can stay. He could give you only 2 weeks.
 
Visiting with intent to stay is fraud as already mentioned.
 
But what I really want to discuss is your plans for your Vet degree. The reason I ask is because I personally know a vet from another country that migrated that could not get licensed to practice in the US (although that was some time ago and he may have gotten licensed since).
 
American medical standards are different. Not saying they are better or worse; just different. Some countries have fewer regulations than the US so there is less red tape to start practicing.
 
The person I know who was a Vet in Venezuela was working as a tech in animal clinics for a few years. I was a hard adjustment for him as he had years of experience and knowledge. 
 
I just wanted to share this story so you can have an idea of the industry in America. If you are prepared to take the licensing exam for the state you are in then you should be fine. 
 
I have a few friends who are Vets so if there are any questions you would like to ask feel free to. 

Aline, welcome to VJ, no harm trying for a B, obviously that aspect depends on whether you can get one. Sounds like you have a 2 Year HRR.
 
What are your plans in the US>

Forget the K-3, it's obsolete now because the CR-1 goes faster than it used to in the past, so a K-3 rarely issued these days.
 
B-2 visa is very risky, you have a high chance of being denied so it might just be a waste of time and money.
 
Like Kieren said: either take the K-1 route (more expensive but faster, however you must marry in the US) or get married in Brazil and go the CR-1 route (slower but less expensive in the long run, plus you get a green card right off the bat if you're approved.) You basically don't have any other options unless you want to risk the B-2 plan which could end up wasting your time and money if you're rejected.

You have to either fulfill the 2-year home residency requirement by actually living in Brazil for two full years (no long visits to the US at all) or get it waived.
one or the other has to happen before you can get an immigrant visa.

A bunch of things you mentioned, some you cant do, some are illegal. Didnt read the entire post. 
 
Either get married in Brazil and spouse files CR1. Or fiance files K1 and if approved by embassy, come to the US and get married within 90 days. 

The home residency requirement can be waived, there is a thread here with many Brazilians there, I think you should check it out before making any plans, to see what's the time frame for it, fees, documents, etc.
 
do you have a b2 visa? If not, getting one might be very hard to get. You not only have immigrant intent, but also are planning to stay way longer than you're supposed to per year. Even though a b2 entrant usually gets a stamp for a 6 month stay, that's up to cbps discretion. Entering one time and staying the whole 6 months, then attempting to enter again in about a month after with intention to stay for another 6 months is living here and not visiting. And if you tell them your intentions in your entry, I'd doubt they'd let you in anyway. 
 
You have two legal options: file i129f petition, go for the k1 visa, enter the USA, marry within 90 days and file for aos OR get married in Brazil (or another country) and have your spouse file a i130 petition and you go for a cr1 visa. Any other plan is fraudulent at this point.
 
take your time, read, educate yourself and go for the right path for you.
 
best of luck

You're right. Your B2 has a high risk of being denied since you probably can't prove enough ties to your home country. Also, if you stay 6 months in the U.S. and then try to come back a month after you leave, that would almost prove you have no ties and any attempt to "visit" would be viewed as an intent to immigrate. I say you wait, finish out you degree in Brazil, have your BF go there and marry, then file for a CR-1.