love without a motive

So there's this guy and I've liked him for about 6 months now. We were serious for like a month, but we still flirt occasionally. I'm really close with his sister, so I see him a lot outside of school as well. He has this other girl he's kind of seeing, but they're not "together", and that bothers me. He knows I like him, but he continues to flirt without addressing the issue. Should I continue to hide my feelings and play these charades or just quit the game?