He's jealous when I talk to other guys- even though he has a GIRLFRIEND?

A guy I've known for a couple months now had been showing signs of liking me, despite being a shy guy. It has been getting stronger with each passing week and he has even gotten jealous when I talk to/pay attention to other guys.

However, I just found out he has a girlfriend he has been dating for 7 months. He never once mentioned her in all of our talks (though I know everything else about him and his family). Because he's so shy and appeared to be a responsible person, I never expected anything like this from HIM.

Despite the fact he is dating another girl (whom I've met before and I like), he still tries to get my attention and gets jealous when I talk to another guy.

What the heck is this guy's problem? What goes through someone's mind to do something like this?
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+1 y
But WHY does a guy do something like this? If he really likes me so much, why didn't he break up with his girlfriend before it got to this point?
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+1 y
Also, recently he's begun to attempt to make ME jealous.
He'll talk about how close he was to a certain woman and how they used to be able to talk for hours.
And worse: he used his girlfriend to try and make me jealous! He purposely cuddled and rested his head on his girlfriend's shoulder DIRECTLY in front of me. -I will note that he wasn't drunk, but he had been drinking (it was a work function)-
He's jealous when I talk to other guys- even though he has a GIRLFRIEND?
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