How do I get over someone who never has, and never ever will love me?

I have known this guy for ages, he is married, but I have fallen in love with him. When Im around him (which is rather alot, several times a week, and I cannot avoid this) I feel the happiest iv been for ages, Im in a really, really bad place at the moment, but he makes me laugh when I want to cry, and when I felt like commiting suicide, he made me realise that there are some things in life worth living for.

But this is realy geting to me now, Il catch myself thinking about him most of the day, I can’t stop myself, when Im not with him everything reminds me of something he said or did, and Im miserable because I can’t be with him, and when I am with him, I get this wierd feeling all over my body, its like butterflies, but 10 times the scale, this happens even when someone mentions his name.

This is realy taking over my life, and I have tried so many things to make me get over him, but they havnt worked, and im afraid that i wont get over him until I find someone else who loves me back (That might never happen). And its not just emotional pain im going through, its also physical, im headachey and nausious a day or two before I see him because I am so anxious. So how can I get over this guy? I realy need to, otherwise i will just go mad.