Why would my best friend be doing that?

He is married yet he always talks to me on the phone texing me and stuff,we will be joking and i tell him to bite me and he tells me that if he bites me he leaves marks?? Then he talks to me on his lunch , break and when he goes home, i ask him if he misses talking to me a day when we dont talk and he says DUH, which apprently means yes.he is not a cheater i known him for 10 years and i know he is not like that does it sound like he likes me more than a friend???To me it sounds like he is not happy, and i cant ask him.