What should I do?I'm hurt and confused?

I have a guy friend that i really like..but he doesn't know it..i've always been there for him.,whenever he's needed me.this week i've been giving him a ride home from school because he doesn't have his car yet..but i also have another friend dat i've been taking to school nd taking her home also..From the beggening i told her that i like my guy friend..I let her know so she wouldnt try to get with him.she has a boyfriend,but she's been flirting with my friend..he's been flirting with her too and he asked her for her number and she gave it to him right in front of my face...i didn't say anything to either of them,but i was upset..and i don't know what to do now..i've been through so much with my guy friend and i understand that he's not mine but it hurts...