What do I do? Should I leave him alone, or go for it?

I had a guy like Mister K. I met him and instantly felt attracted to him. He was unavailable however, so I started dating other guys. Every time I would meet up with him again though, I realized why I liked him so much. If he had been single (AKA, your situation) I would have gone to him in a heart beat. Honey, I know your confused, but follow your heart, there is a REASON you keep falling for him and going back to him. GO FOR IT!