Something wrong with me?

I (20M) have only been dating my gf (20F) for 2 months. It’s going great but I’m already doing what I do in every relationship, self sabotaging..by that I mean I am ridiculously jealous and having trust issues (she will be going back to uni in the fall). I have always been jealous about past partners she has, I don’t know how many or who which I prefer but I am constantly thinking about it. We talk about things we like during sex and I can’t help but think about her doing those things with others. I know it’s in the past and it shouldn’t bother me but it does.

She has given me zero reasons to not trust her but my last relationship had some nasty cheating and I think that has destroyed my ability to have trust in someone being loyal to a relationship. I am extremely stressed out about her going back to school and although we agreed we can do long distance I know that stress is going to result in problems.

Why can I not get over her past partners even though she clearly has zero interest in them now? And is it fair of me to bring up the trust issues even tho they were caused by my ex girlfriend? Do I need to go to therapy?