Am I doing something wrong?!

Please let me know if I am approaching this the wrong way. I like this guy I work with. I am pretty sure he is gay. He seems to be flirting with me. He asked me to hang out with him. We went out for drinks and then to a concert. He has my number but has only texted me once. I feel like he sending me mixed signals/or maybe he's just really friendly, and it just seems like something more bc I am generally antisocial haha. Anyway, I am trying not to appear to clingy/desperate. I texted him on his birthday, and gave him something cheap but nice for the holiday, and made it appear as a friendly gesture. I try not to over do it with the talking, and try to appear a little stand off ish.TLDR: So here's the question, should I play hard to get, so I don't seem desperate/clingy? Or, should I reciprocate his gesture and ask him to hang out, even though I don't know what his angle is or if he's in a relationship or w/e? Would it be weird to ask him to go see a concert on a weekend?