Why do married guys cheat?

Ive been working at this factory for about 2 years now, and there is this guy who has been very flirtatious with me, it started as just playful smiles and banter, but it has went to a new level. Now he wants to take it even further, why would he have drudged this out for 2 years just for ?.....i didn't think a guy would wait that long, btw he is married, and im pretty sure he ain't getting it at home, one more thing, wouldn't there have to be some sort of physical attraction, there i mean a guy wouldn't just wanna F### an woman he found really ugly right?....im trying to figure out why he is interested in me.