How do you know your in love and not just lust or infatuation?

I think I fell in love with a man I cannot be with, for personal reasons, and he tries to stay away because he knows there is no light at the end if the tunnel. We are both really the same and completely opposite in a way I cannot explain no matter how many times I try to be concious about it and explain it to myself over the course of 4.5 years now. Everytime I say to myself if I do this I will forget him and with time it will get better, but it only gets worse!! I've never felt this way ever in my whole life about anyone. He just seems to be unperfectly perfect for me!! So is it because I cannot be with him that this is happening? Or is it really love?
How do you know your in love and not just lust or infatuation?
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