Someone help me... relationship

When do things get better ? When does the constant fighting stop ? When does the trust come back? The last year and a half have been absolutely hell between us. Things really went down hill when the fighting got really bad. And if that wasn't bad enough. I have pretty extreme anxiety and depression. Along with trouble at work and family. And having depression for so long it just takes a toll on you. It all got so much that I tried to take my own life. And in the time of recovery from attempted suicide the boy that was meant to be by my side left me. He started drinking more, he started smoking, he even gave his phone number out to another girl while we were still together. While I was at home falling apart. He started following girls on social media. The kind that post provocative photos. Would flirt with other girls while drinking and getting drunk with friends. 3 months down the track. He said that it was wrong and that it won't happen again. How do you know it won't. How do you over come something like this ? I consider it cheating. He doesn't. And get very offered when you consider it as cheating.

But how do you rebuild trust after something like this ? How do you forgive? How do you forget ? It gets to the point where we will be fine for a few days then it just plays on my mind and I'll get upset and bring it up and it causes a fight where we don't talk for a few days. It's ruining our relationship more and more. Because I can't seem to forgive and trust him anymore. How do you over come something like this ? I want things to work out but it's so hard when I could be having a really good day or be at work. And I'll just start thinking about what he did and it just hurts and ruins your whole day. Then you talk to them about it and it starts a fight ?

I don't want to end things because I love this boy so much. I want to know how to learn to trust him again and forget about it but I can't. Please help 😕 I'm tired of being hurt. I just can't seem to let it go I want to more on from it but I just can't 😪.