I worried that I have a crush on my boyfriend's close friend
Why do you have a crush on him when you have a boyfriend?
My boyfriend wouldn't want to be in a relationship with me then, I'm in a relationship with my boyfriend because he said he wouldn't tell anyone about my secrets.
You shouldn't betray your partner. He loves you and it's wrong to crush on his friend like that.
It's not important since he will never find out since I'm not stupid enough to tell him.
Just because you won't tell him, doesn't mean that it's okay to have these feelings for someone else. I believe it's wise to try to stop these feelings and get on with your boyfriend. How will he feel if you started to betray him and make his friendships awkward?