I don't know what to do

So, I've liked this guy since I first saw him on the second day of school in August. I just recently found out that he has a girlfriend but he has been dating her since before school started. He doesn't talk about her much but since we're good friends, we talk about basically everything, I want to tell him how I really feel about him but I'm not sure if I should or if he even feels the same way… what should I do?