He wants to leave his girlfriend for me...

and I feel uncomfortable with this for some reason. Until recently we had only been friends. But he recently let me know that he likes me and wondered if I would give him a chance if he didn't have a girlfriend. I guess it just makes me think that maybe if we dated and he got bored with me or we started arguing, he would leave me for somebody else. Does this seem like a valid conclusion?

Oh, I should mention that he wanted to go out with me over a year ago (before the current girlfriend) and I turned him down. I didn't know him then, but we have become friends within the last 6 months.
He wants to leave his girlfriend for me...
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