Hes got a girlfriend

I'v got myself into a bit of a pickle.

I liked this guy (who i;v known for a few months) , and he found out and he likes me too, so he asked me out on a date and we're going in a few weeks. However, I'v recently started getting really close with his best mate (who i've known for years and years) and I cant stop thinking about him. Hes got a girlfriend, but I think thats gonna end soon and last nite we were up all nite texting and he always says nice stuff about me... I dont know what to do cos i dont want to hurt anyone. Anyone got any advice?

Thanks