simple. He knows you're attracted to him and were at one point involved somewhat. He's showing his true colors right now in that he likes to keep other women on the hook. Whether it's for his ego or outright potential cheating does not matter one iota. Fact is he is showing who he is with the current gf so... there is no good outcome to this. right now he's doing his current gf wrong by contacting you and being flirtatious. He's doing you wrong by using you for his own ego or other reason. Even if you at some point were interested in being involved with him again, you've got to stop and think, with knowing how this guy is, do you really think he'd be any different with you or any other person he was involved with? and that being said do you want to be a party to his obvious deceit with his current gf? I'm not implying you've voluntarily been a part of it, but that knowing what you do now, the best bet and right thing to do would be to cut it off, block him and move on.