Why did he say "you deserve better than me"?

I have a guy friend I hang on with occionally, we're both in our 30's unattached, and divorced with kids. We are not bf/gf but we have been intimate a few times, and he's basically a great guy to be around. We got together last week and after he left, I sent him an im thanking him for the pizza/movie, that I had a great time...and how i liked him alot. I saw no problem with this cause he tells me he misses me all the time, and the too likes me alot. I got a thank you but you know you deserve so much better than me. This came out of nowhere. We aren't dating, just friends so I don't get it....what was this supposed to mean??? I havent talked to him a few days (sorta giving him space) ....do i resume the friendship but don't hang out as much? I'm a bit confused!