What type of guy is prone to getting cheated on?

I have a terrible record. I've been cheated on all three relationships I've had. I'm starting to become cynical about the relationship/dating thing, and by the looks of it, might be walking into a fourth time. I go out with what I think are good girls; modest, smart and church going, and I'm not a loser, I have a degree, make 65k a year, and I'm physically fit (enough to run a marathon). Any tips?