I'm getting hot and cold behaviour from this guy, it's driving me insane. Why can't he just decide what he wants and be normal again?

Clearly, he's very into me. He gets starry eyed around me, nervous, trips over himself, imitates how I speak, what I like, tries to get closer to me physically, tries very hard to make my friends and parents like him, admires my success, does me favours, making late night calls when he felt guilty for something, he stares at me seriously all the time, smiles all the time, the list goes on...

I'm a 100% positive he finds me very attractive (he said so basically), but also that he's emotionally invested. He gets jealous and weird around other guys, he worries for me easily, he's easily hurt whatever I do.

Here's the catch - he has a girlfriend, which I didn't know in the beginning. Since I found out, I've kept away, but we just see each other in everyday life. Sometimes he's talking about her out of the frickin blue without any context whatsoever, then other times, he's almost ashamed to mention her and tries not to do so and seems very careful with "my feelings".

I'm not even into him anymore, don't worry, but his behaviour is driving me nuts cause he's making it literally impossible to feel normal around him. Or be friends. Socially, this is a desaster, we're in the same friends group, but no one else knows what he's done when we're alone. He's either making me aware of how hot, intelligent and wonderful he finds me, I'm being reminded of that every time he's weird around me and tries everything he can to impress me and be "my type", OR he's being a d*ck who keeps talking about a girl I don't know, making a big and WEIRD effin deal out of it. Sometimes he's just weirdly cold, for example: one week, he talked about throwing me a birthday dinner - and afterwards, he's literally about to UNINVITE me to my OWN birthday dinner my friends wanted to throw. The heck?

Can he PLEASE make up his mind?
It's exhausting to pretend everything's fine, it's like gaslighting! I'm pretending for his relationship's sake, yet he treats me like this.
I'm getting hot and cold behaviour from this guy, it's driving me insane. Why can't he just decide what he wants and be normal again?
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