Me (20M) doesn’t know how to fix my relationship and keep going with my (20F) girlfriend

I know this is long, but I’m coming here because I really need advice for my sake in the relationship, and my sake mentally. I’ve know my girlfriend for a year. We finally started dating in February. It was my first relationship of my life. Everything was great but a month in everything hit. I got scared of being in a relationship since everything was new to me and I panicked and broke up with her in March. Now that night, all of our friends are were yelling at me (and rightfully so), so later on I went to my neighbors (college apartment neighbor) who is a girl to talk. I needed someone to talk to and she was the only one that would listen. I ended up staying the night because she ended up falling asleep during me talking and I was like wtf I guess I’ll go to sleep there instead of going home. Nothing happened, nothing. I understand how fucked that is going over there, there’s no excuse break up with my girlfriend and sleeping over another girls place (I shouldn’t of gone in the first place, and I definitely shouldn’t of stayed) In April, since me and my neighbor were friends, I stayed over a couple weeks later 2 times and we made out but nothing else (I slept over one time before me and my girlfriend were even talking but still I never had sex with this girl). I was still talking to my ex, as I wanted to remain friends with her after we broke up because I knew deep down I wanted her, I was just scared of a relationship since it was my first. There were times we had sex and she slept over, and I realize doing that with her and sleeping over my neighbors at the same time is completely messed up Towards the end of April I fully realized how I love my ex girlfriend and cut off my neighbor completely, and in the beginning of May, me and my ex were official again. Before we got together, I told her how I slept at my neighbors, and she was upset but said it’s in the past. Yesterday, we were talking about the past, and I brought up my neighbor and that exact situation how I regret sleeping over there and making out with her later on in April. My girlfriend ended up misunderstanding that situation that I told her before we got together, (as she thought this all happened before we were dating) and she said we’re done. I ended up driving a couple hours to see her and we talked it out, she said she needs to regain trust in me to keep this relationship. She’s 100% correct, I shouldn’t of went to a girl to talk when we broke up and I shouldn’t of stayed the night the first time. I shouldn’t of slept at my neighbors later on 2 times and making out with her (yes I was single but it still wasn’t right and I have to live with myself). I truly realized how much I love this girl in May and that’s why I got back with her because I want to be with her forever. I don’t know how I can live with myself knowing I hurt her by breaking up with her, and making out with another girl when we were broken up. TLDR: I’m not asking for forgiveness, I messed up. I will die by loyalty, I never done anything bad when we were dating, this all happened during a month we were broken up. I just need advice on how we can make this work and how I can tell myself I need to forgive myself. Thank you.