Self loathing/harm/guilt

I don't have a bad life... But I have made some mistakes recently that are eating away at me. I cheated on my ex and then I left her because we werent a god match and I knew I broke her heart. I can't seem to forgive myself. I feel like a shitty person and I miss her every single day. It's been a month and today I fought, successfully, the urge to self harm. I have so much going on in my life right now - my mom has a double masectomy in 2 days and I'm studying for the most important exam in my life. I have to force myself to focus on studying at least 8 hours everyday. I'm not sure what else to do.... If the self harm urges continue, eventually I will give in when my emotions are intense enough... It's awful, I know, but I get satisfaction from seeing blood which scares me. I switch between loving myself and hating myself. I constantly remind myself that I am not one mistake but it doesn't change the fact I hurt her.