Cheating + mental illness

I was diagnosed with chronic anxiety and depression about 2 years ago and have recently just gotten back on my meds. I have also just found out today that my boyfriend of 2 years got drunk and had sex in a bathroom while being away for work since we are in a long distance relationship. I'm feeling completely lost with what to do coz I still love him, but hate him for what he has done. sex is a massive deal for me since I lost my viginity to him and I see it as a sacred experience just for us. We are both 19 and his mum believes that he is young and dumb, but if I truly love him that I shouldn't walk away. I don't know what to do or feel anymore. All I know is that I don't want to ever feel this much pain again. Please girls I need your advice xx