It really wasn't fair or correct what your mom did to you. Your bf may have hit the nail on the head saying that she is jealous. Sounds about right to me. Regardless of the reasons--- there just aren't any good ones. You sound like a great person -- brave and strong. I hope you see that.
When you are never allowed to feel part of the family it makes it hard to understand how it feels to fit in anywhere. Your mother gave you such negative feedback from the time you were little that it's amazing how well adjusted you seem.
If you aren't seeing a professional you may want to do so. I've never been in therapy myself because it isn't available where I live but people here say it really helps. I would hope that a therapist could show you how healthy relationships work and guide you to seeing things clearly.
You sound like you do understand that you are not responsible for the way you were and are treated. I think that's an amazing step to have made on your own. With insight like that I'm sure you have the inner tools to grow and learn to live a healthy life.
If you don't want to break away completely from your family maybe it would be good to stay away for a year or so till you are in a position to withstand your mom's ugliness without pain.
You sound like a really wonderful person and I'm confident that you can build a good life for yourself. Anyone in your position would need some help sorting out your feelings so try to find a counselor or therapist to talk to.
Good luck and keep posting here. We will give you as much support as we can.