I cheated on my LDR boyfriend with my guy best friend...who is also taken

So I've known this guy for ages, we basically grew up together. We went to a party together, got drunk, one thing lead to another and he kissed me. After that he didn't seem to regret it too much, I assume because he was drunk. Next morning he texts me saying it's best for everyone that nothing happened last night, and to just pretend it didn't and continue or friendship. So I agree, because he means a lot to me as a friend and I wouldn't wanna lose him over this. Couple hours later he texts saying he's been thinking about it and decided it'd be best if we stopped hanging out. So I'm obviously like wtf no, and somehow convince him to keep the friendship going. 2 weeks pass i ask him to hang out, he tells me that he told his girlfriend and she's pissed (understandably) and wants to stop hanging out. I again manage to get him to go out and talk about the whole situation, clear things up, and then decide what to do from there. I even suggested talking to his girlfriend so I can reassure her that there's nothing going on between us and that it'll never happen again. He seems very hesitant and I'm so confused and scared idk what to do