whys this cancer man being sneaky?

He has a girl friend currently but I'm getting the vibe he tries to find whatever chance he can get to be near me. For example the other day he came into my work (twice) within a couple hours. He's always trying to make conversation and find an excuse to linger around. He even flirts with me etc (he would never do this in front of his girlfriend).

I've noticed he's even started purposely ignoring me on social media.

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He's not happy so he is seeing if he still has his mojo. Or he might think you're cool. I'm a chick but if someone is cool I try to befriend them. I think you should put your foot down and some boundaries and ask his intentions.

This is not a cancer thing. This is a "sneaky douchebag who isn't happy in his relationship and doesn't know how to be alone" thing. Whatever his intentions, don't try anything more than friendship with this one.