Well it depends,
If u dont get love, attentions, sex from home
then more likely u will b looking for those outside home.

Most cheaters have huge egos and are hurt easily if you don't pay attention to them all the time. They have no problem hurting others, in fact, it makes them feel like they've got power. You can also tell by their last relationship. If they got with you before they broke up with the last person, they'll probably do the same to you.

As far as someone checking out others in front of you, it's hard to tell if they're a cheater just by that. They are disrespectful as hell which is a good breeding ground for cheating. There's no reason for someone to do that to you. If they lie alot, yeah, that's another great sign that they might cheat. Best find yourself another guy who is a little more secure in himself and doesn't always have to find if the grass is really greener on the other side.
http://infidelity-concerns.com