Me [27 M] maybe going for a relation with [20 F] - My trust issues are making me unhappy

Currently I'm seeing a girl. This is for about 2 months now. At first this was more casual. I'm always open and honest, so she knew that. At that time I was seriously not looking forward for anything more than casual. She has accepted that from the start.

My own reason was that I ended my previous relationship about 1-2 years ago because I was unhappy. I was unhappy with myself, the way I thought. I will go more in detail about this later. The main point is that I didnt thought myself ready to commit again (still do actually).

As things obviously can go, I really started to like this girl. The feeling is mutual. We have talked about this (tiny future steps) and we both were really honest. She does not know what to expect from me, and I told her my "issues" and doubts. Not doubts in her, a relation.. but my own feelings and behaviour in a relation. I guess we both understand each other and are willing to let this work.

When things get a bit more seriously, I really get a shitload of trust issues. They are there for no reason at all. It just starts when I really care about a person. I'm having a hard time doing my own stuff (hobby etc.) and she or the relation keeps popping up in my head. I cannot even enjoy the fact that there is someone I care about. All my thoughts are negative. In my mind everything she does is sort of "wrong" or not the way I think about it. I really hate talking good about myself, but I'm a nice guy. I actually hate myself for thinking the way I do sometimes. It even makes me sort of sad. That was also the reason I broke off my previous relationship.

In my mind I had 2 options; 1: be a complete ass, push my own thoughts towards her, act the way I want, control her, etc. Or 2: break it up and let her be happy the way she is / deserves.

I had to pick 1 of the options to be happy myself. I cannot be happy if my partner is not happy because of my actions or how I act. I honestly do not want someone to change for me. Sure we both must adapt to each other but thats it.

Now I feel there should be the 3rd option: fix my thoughts. I talked with friends about this and most people say I really need to talk with her. Express my feelings and such. I really do this, but it has zero effect on how I feel.

A real example is that I have issues with how we communicate. I expect things from her. If we talked about meeting up on a saturday but she does not know if she is able to make it and comes back on it.. I expect her to actually come back at this subject. I guess that is really normal. The thing is, even if she does.. I always have something negative in my mind about what I do not like about it. Even if you express and communicate perfectly, I will find something that annoys me and it keeps sticking in my head.

Now the issue is I guess for every girl I will ever see. It has nothing to do with her. Yet I really want to fix this but I have no idea why. I thought about my previous relationships and I guess 1 sticks out. I had a relation for 2-3 years and she broke up really sudden. She wanted to move back to her birthplace where her friends & family were. She never really expressed her feelings about that, never talked about it, till it exploded and she broke up and moved out within a week. I guess that's really the reason why nothing is good for me. I always lived with the feeling I had a good / decent relationship and it so suddenly stopped. Therefore even if someone communicate with me, I always have this doubt in me, and I will keep looking for things that are off.

I hope people can help me with dealing with this, I really want to be happy in a relation.

tl;dr: In my past someone broke up with my suddenly, I guess I got trust issues since then. Everything seemed fine and that sudden move really hurted. Now days even the real "good" is not good for me anymore.