Will he ever leave her?

I work with this guy who has a gf. Yes I know it's wrong but he likes me. He is always telling me I'm hot and kisses me and things like. He's shy at work and doesn't really talk to many girls so I know that he only does that to me he's not a player!! Anyway, he has a gf, and I have a feeling the only reason he's with her is for their daughter. He said they fight a lot and have been together 5 years. I'm playing it cool and just never bringing up the subject about him leaving his gf. If I ask him something he just prefers not talking about her......I feel that he really likes me because we go to lunch together (he buys) he tells me i'm hot and we are ALWAYS texting even if he's home with her. That makes me think that he is risking a lot to talk to me. Right?? What bothers me is that we NEVER ever see each other outside of work hours. He may go in early or leave late but that's about it. He says " you know I can't" .. He's with her on the weekend and on evenings. I hate that he acts like they're a happy family when they are not. Am I being a fool? Will he ever leave her? If he loves her why would he be with me? We only had sex once in my car. Other days we just fool around. Another thing, he will not add me on facebook! He said he doesn't like to add people from work. But the other day another co worker and him were laughing about a post he had put... Please can someone give me advice? I knw that he's a good guy. btw we are both 23 and she's 27 I think she may be too "old" for him??? Thanks