Can I forgive my best friend for these lies?

I met my friend through another friend, who subsequently disappeared off the map and that’s how I got so close to this new one. in the start everything was amazing hanging out, chilling, talking, whatever it was great and relaxed. Then I introduced him to a mate (someone fitter than me) and nothing seemed to change. We slagged her off because she’s annoying buy I noticed something between them so I would ask him every so often if there was anything, the answer was always no and i believed it cos there was no reason to lie, he hadnt before. a few things happened that spiked my interest after that, id ask him about them but still no reply so fine, wateva. then about 6 months after the introduction we got wasted and ended up sleeping together, we decided not to tell my friend (i thort) because she had a crush on him and i dint want to hurt her feelings cos it meant nothing. everything was goin fine, situation averted as u could say, till one day he blurts out to me that he ‘touched up’ this girl. shocker but what could i do!? then she dedides to tell me all the gorry details, it was at least once a week for the whole summer. since then all i can think about is them together and the lies, im not quite sure what i need help on but please!!! is there anything that can be sed to this?! something to say to him or an insight into his brain?!?!?! im finding help in alcohol and apathy…i cant do it much longer the tension is killing me,

sorry for the length but its a real problem that has arisen right before my exams and i need a good sober nights sleep!