Man?!?

I know that not all man are the same but I don’t get it why do they cheat on there wives. When they have a family and kids and all but still look for other things outside the house. I really don’t get it. There’s this dude at work who has been married for about 8 yrs and has 4 kids and a beautiful and nice wife. But he is hooking up with 2 chics from work. He was careful at first but now people are talking about him sleeping with 2 chics from work at the same time (not sure if together as a 3some) but yeah I’m like really dude?!? I’m a single mom but bc of this sometimes I rethink marriage bc man can be so selfish and stupid!!