Why men cheat?

The new trend of men cheating,especially nigerian men has become something really serious, talking from personal experience. It's almost like a norm in every nigerian relationship.Is the same for all my friends that I know.At first even without kids the guy will cheat and after like two kids they become apologetic about **it** and even shout or walk out on you when you try to confront them.Its so heartbreaking that most married woman are married but very lonely,their husbands no longer has time for them.I for one am struggling to learn to live with it,is not like there are many choices,how someone husband just goes about cheating with no conscience whatsoever.