Used sexually by my old friend…

Hi guys, I need some advice (it is going to be a long story, I will try to keep it short) (also, the contention is not ‘is he gay’, don’t worry i’m 20 and not looking for that advice )
So let me set the scene for you. Twas a boy of 17, going through serious depression, and while on the pills I made some terrible decisions which I still to this day regret (20 now, been off them for a year!) my sexuality was not the only reason for the depression, abusive alcoholic father was a main reason. Anyway I came out to this guy frank that I was bi. He was cool with it, we chatted for 2hours and all was good, told him I didn’t have feelings for him yada yada ya. Next day we chatted some more, told him about my dad and all that good stuff (my two dark passengers). Now Frank was always very flirtatious with guys, but was ‘straight’ (had girlfriends ect. His sexuality is not in question). So we were lying next to each other smoking as we always did, then he came on to me and unzipped his pants. So we did things, for about a week or two. Looking back on it now I know he used my totally fragile state (I know I could of said no, but as I said I made a lot of wrong choices, what done is done, i am a bit slutish deep down lol) to get what he wanted then fucked me off when he started to see this slag. I never developed feelings for him, I could not feel at that time.
So we stopped and a year went pass, on and off friendship (silly reasons), never touched on the subject as if it never happened. I got better once school finished, learned to cope and started to see things through the fog. He went on and off with his girlfriend (who he was living with) and then had to move in my with my best mate (Mike) once it was over (also his best mate…so this is where choices start to diverge and help needed), they both tried crack, frank lost his job, both got off it and frank moved out of state. Me and Mike rekindled our friendship which was strained and we have been great. I am almost back to where I need to be (don’t think I ever will, but then again, strong chance I am romanticising the past), life is good. Find out from mike that frank is coming back and most likely moving in with him again. The last three times I was with frank, it was in the extended group setting and I said all of 5 words to him, I didn’t waste my time or energy dealing with his shit. (did I mention mike knows I am bi, but has no idea about me and frank? Yeah, my bad*)
So this is where I am at. Frank used me, tossed me aside and went downhill (karma?), me and mike best friends. Once frank moves back he will be with mike all the time, thus If I want to spend time with mike I will have to see frank. I don’t really want to see frank, we have a lot of common friends but they don’t like him, he is seen as mikes friend (+1 for me)So….need suggestions: keep in mind telling mike is totally out of the question, he has too much in his life to worry about this kind of bullshit.
So any help would be very much welcome. If you need any more information please ask.