It’s fine for this being really long, it’s better that you’ve sent everything instead of hiding stuff.
Okay, so first of all you need to sort things out with your current boyfriend. It sounds as if things are just not going to get any better if you don’t talk about it with him. In the end you need to either end the relationship and both move on, or just continue to -pretty much- lead him on and act as if everything is fine. The second choice is a bad choice, so go for the first one or try to sort out your problems as a couple.
And with the second guy, your “best friend”, before anything happens with him you need to sort out your relationship first. That’s your priority at the moment. If you and your boyfriend do happen to break up, don’t just go running to this friend of yours as your boyfriend(well ex boyfriend) will just feel worse, so at least wait a few weeks. Buuuut.. I would also try and see that when you are single if everything is still the same with this friend as it was when you were in a relationship, as it could just be the “forbidden fruit” scenario and you could just be having these feelings for him since you have been in your relationship for a very long time.
You have a lot to think about before doing anything, just don’t rush into anything without thinking.