Maybe. You may be denied ESTA and would need to apply for B1/B2, which is never guaranteed.
Yes, you're starting from scratch.
You need to think about the following things:
1. Are you sure this is the right relationship to be in?
2. Are you sure your fiance has a valid point or is he trying to control / manipulate you?
These points are super important, because if he is a manipulator, you'll face this again during:
1. Visa process
2. AOS process (if you're gonna go via K-1 again)
3. Removal of Conditions
Either way, you can still marry outside of the US and get a spousal visa next time, which is a superior choice. You may have to put extra effort to prove your relationship is genuine because of not proceeding with AOS now.
Very sorry to hear you had a big argument. Immigration is stressful, so is the new relationship. There's new challenges for him as well as you.
If you still have time, you can discuss what's the best for two of you.