Why do former flings sometimes come back?

I once hooked up with a guy, and a few years later, he texted me some sexual stuff about my breasts, body, vagina, and appearance. He had a girlfriend, too! What gives? Why do men sometimes do this... like I said, he initiated contact years down the line, and I was never interested in him in the first place... and he had a GIRLFRIEND!
Why do former flings sometimes come back?
Post Opinion