GuyRule #549.0: Cheating
If you decide to cheat on your girlfriend for some reason the girl that you do must be at least twice as hot. If the other girl is your ex, cheating must be limited to a maximum of 3 times, otherwise there is a danger of the ex getting too involved and screwing up your situation.
And if your woman is extremely hot or if you are married or both, don't cheat, because:
a)You have no reason to,
b)If it ever gets back to her, you'll regret it for life.