Do we ever ask the guy why?

There's a group of us that hang out together but I m pretty close to one of the guy. We both like each other n open abt it but Never dated . There's another gal in the group which they kind of dated for a while.. after a while he left her but we all still hang out as a group..I m seeing him sometimes on weekend but we are still not dating.. I feel kind of jealous n hurt that he kind of drop me for her even thou we are seeing each other in some ways. Bk then he talk to me abt her n y they can't b together. We talk abt all kind of things. I m wondering should I ever ask him y he choose her over me in the first plc. It kind of bug me but should I just let it go n move on