I can definitely relate to this because I have a guy that is a really close friend to me, who flirts with girls. One of the girls that he flirts with is a close friend of mine and it makes me upset. I just act like I don't see it happening and that I don't care. Most people know how I feel about him. but still try to make me upset by flirting with him. I just have to put on a good smile, and continue on with my day. I still don't think i'll ever tell him what goes through my head when I see him with other girls flirting. I guess I will always be friends with him.