(20M) (20F) How can I stop my girlfriend from doubting our relationship?

My girlfriend and I have been dating for 3 years now. Let me preface this by saying I have 0 feelings for my ex and have no desire to see her again, and love my current girlfriend more than anything. About 5 months in to the relationship she was asking me questions about my ex while we were drunk, and I admitted to looking at my ex’s Instagram profile once out of curiosity while I was dating my current girlfriend. Obviously she was not happy about this. We voiced her displeasure and we talked thru it and that was that. Then like a year later I was with a friend and he thought it would be funny to look at my ex’s tiktok, which had a lot of corny things on it, to make fun of her. And stupidly, I did it with him. I also did not clear my search history afterward and my gf found it while i was letting her use my phone.

Again she was pretty upset by that, understandably so, and I vowed to never do it again. And I haven’t. Anyway after that incident we were doing long distance for 6 months as I played junior hockey. She hated long distance and was pretty depressed. 1 month before I returned home again she called me and tried to break up with me. Her reason being she still had those lingering doubts I would stalk my ex again and they wouldn’t go away no matter how well I treated her. I convinced her not to. That I would be home soon and things would be better when we’re in-person again. I came home and for a few months things were good, but I wanted to attend an out-of-state college next year to play on their hockey team and thought she would move with me. But she decided moving wasn’t in the cards for her and tried to break up again. The only reason in this convo being that we have different goals and career paths and she wanted me to attend this college but it couldn’t be with her and she couldn’t do long distance again.

Under the impression that long distance was our only issue I found a lower-level in-state college team to play on and canceled my commitment to the out-of-state to be with my gf. And we’ve been getting along really well again but my gf just has doubts, which I found out last night. She says since she’s found the courage to try to break up with me twice the relationship doesn’t feel the same anymore. That part of her feels she did fully breakup. She admitted that I have been treating her really well since our problems and haven’t given her reason to doubt me again. But because she’s tried to break up twice there must be something wrong with the relationship.

Anyways I know our relationship might be over. But it’s such a punch to the gut when we really have been getting along so well and I burned a bridge to the college I wanted to stay with her. We’ve never fought or had arguments about anything other than this so it feels like a mistake to me. And most of this ex stuff was over a year ago. She told me she doesn’t even doubt my loyalty anymore, so the only issue left remaining is that the relationship feels off now for her. Is that something that can be worked thru? Something that would go away with time with me being the best boyfriend I can be and being in-person? I don’t know what to do

tl;dr: our relationship feels off even after working thru previous problems and my gf still has doubts