How to solve a love triangle?

Okay so I am in this love triangle. I have been with a guy for almost four years & i have feelings for him but they are starting to fade. I have grew attached to him & it is so difficult to leave him. But the other guy is my best guy friend & we have been friends for about three years, i just can't see losing him. But my boyfriend doesn't like him at all & doesn't know i still talk to him. I have chose my current boyfriend over him 3 different times & he is still talking to me so I know he cares so much. & i have developed strong feelings for him. But I want to know how to leave the other person without being so hurt, because if i don't do something soon I think i'm going to go crazy and so is my best friend.