Just walk up to him and say this,
"(insert name) I'm sorry and pleasedon't hate me, I kinda... Well, really like you... I know you're with my friend and I really don't want to break you two up even if she wants to make me jealous because she knows that I like you but... I'm really. Truly. In love with you. I know you won't accept my feelings and the flirting back is just a joke, but yeah. I like you a lot. Please... Don' hate me."
And act like you're about to cry.
._.