I like my friend, what should I do?

Ok so me and my ex broke up about 3 weeks ago, and he told me he likes this girl named kelsey. Me and him are still really good friends, so we still like tell each other everything. I have been friends with his one friend Josh since the beginning of the school year, and we always flirt with each other. But my ex and a lot of other people told me that he also likes Kelsey. My ex and him are in a huge fight over this right now, and I really like Josh. He still flirts with me all the time and everything, but I don't know what I shoudl do.