It sounds to me like he rather enjoyed you chasing him and to be telling you that he likes one of your friends, he's hoping that you'll all of a sudden decide you don't want to be with current b/f and start chasing him again.
My guess about why it's bothering you is deep down you're maybe thinking "why couldn't he have been this forthcoming when I liked him".
I understand why you wouldn't want much contact with your friend if they got together, I've been there and it's not a pleasant situation to be in.
Sweetheart, try not to let him get to you, you know you've got it good with current b/f and this guy is just being a tw@t.