What does it mean when a guy tries to make you jealous when he is with a girl?

This guy used to flirt with me a lot and I was curious if he was playing or really interested. He was out of another relationship, but to be sure I sent him an email asking if he was interested and if we could chat sometime. He ignored my email and I wondered if it backfired on me somehow because now he is trying to make me jealous that he is with a new girl. I do nothing to get his attention, I lost interest in him but he goes out of his way to flaunt and be affectionate with her in front of me. She acts the same way. I thought this was maybe a cowardly way to say he's not available instead of emailing me back, but why still flaunting her? Is it possible he is still interested in me, playing with me? Or does he feel the need to drive the point home that I'm still not over him? He treats me in a love/hate way--like he tempts me, but wants to see me suffer that I don't have him and someone else does? It's hard to avoid seeing this person so I want to know what's the best way to deal with this behavior? It bothers me not so much that I'm not with him, but that I'm still single and behavior like this is hard to deal with sometimes.