Well, this is just me, but I'd talk to him about it. Straight up "hey you know I like you, and I know u have this thing with ur ex, but I need to know where our relationship is going." Because, if you like him, you need to know if he feels the same so u don't waist ur time. If he does, tell him where you stand on that previous gf matter. But that's just me , so I'm not sure if you want to handle it that way.