He called me his other half?

My best friend [he's a guy, PS], and I always say that we love each other and stuff, and we call each other our twin, cause we have the same birthday.

He said, in one sentence, "you are my best friend, my twin, and my other half."

...I don't get it Dx
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I want him to like me, so I'm confused about it. I don't know if I should make a move or not. I'm normally really really shy around people in general, but I feel more comfortable around him.
He called me his other half?
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