What can I do about a forbidden crush?

I have feelings for one of my boyfriend’s close friends. I’ve been with my boyfriend for nearly a year, and been aware of the crush for about half that time. It got really bad when a group of us went on vacation together and I had more time to really talk to the friend. I don’t consider myself a sappy person, but I treasure even small moments with him and I keep thinking about him when he’s not here. He’s a really warm and genuine person.

I came clean about everything last night to my boyfriend (the three of us were together, but I talked to my boyfriend alone), and went home feeling awful and knowing for sure that it was really over. My boyfriend called me today saying he isn’t mad and isn’t threatened by this at all, and that he cared about me and wanted to see me. This sweet and understanding conversation only made me feel guiltier. I tried to do the right thing last night by walking away from both of them, but seeing my boyfriend again is really tempting. I spent basically all day crying until that phone call.
Ugh. What can I do?