the other night my best friend admitted for falling for the same girl as me, and he knew clearly that i've been holding my affections for her for some time now. i'm not exactly an open guy, im fine with being around girls and talking to them, but going further and establishing a relationship with one has always been an extremely difficult subject for me. im really self-critical and insecure of my ability to actually be a decent boyfriend.
Tell him about your feelings of loyalty. If need be, neither of you should make a move.
Whatever you do, talk about it.