Hey man, I think the first thing you've got to do is tell your buddy that you sort of fucked up with the whole AMOG thing, buy him a beer, and then put the decision on what to do in his hands. He's your buddy, so I'd say you owe that to him if you want to maintain that trust, and unless HB(a) is "the one", that's more important. About 8 years ago, I was gaming what is still to this day the hottest girl I ever had a chance with, and my buddy pulled the same AMOG shit on me, nailed her, then broke up with her like two weeks later. We're still like brothers today, but I STILL get bitter about that one and bust his balls from time to time
Now, there's a chance that your buddy might get bitchy about it and insist on getting back in the drivers seat with HB(a) or that both of you move on, but that would be retarded. It was only chance that decided you each would pursue the HB you "chose", so don't be too confined by that. If you have a chance to influence things, you should definitely accept that circumstances change, so shift and close with HB(a). Then help him with the other HB. If you pull it down, you guys actually show another side of your game by having the flexibility to adapt, so all is good. By putting the decision on what to do in his hands, you shouldn't be worried about the trust thing, and you shouldn't let him forget that if he gets bitter about that down the line.