I suck at talking to guys that I'm interested in. Help?

I'm really shy, and just generally socially awkward... but there's this guy that I'm interested in, and when I talk to him I tend to get a little tongue tied and more awkward than normal.
I'd really really like to be able to have a normal, intelligent conversation with him, but I get flustered, and self-conscious, and start rambling on about nothing...
He's older than me so he maybe (?) picked up on the fact that I'm attracted to him, but he also thinks that he bothers me... How can I let him know that he doesn't bother me, and have a decent conversation with him?
I suck at talking to guys that I'm interested in. Help?
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