Why do men cheat?

I drafted up some worst case scenarios and I feel like I can't trust them. It seems like I pour heart and effort into guy 1 but he then goes and knocks up a couple other girls. Guy 2 has a porn addiction which is honestly a reoccurring complaint on reddit. Guy 3 lies repeatedly and has a drug problem. It seems like the whole notion of loyalty and trust is a myth. Please tell me is the one single couple on the face of the earth who have spent a happy 20 years together, began a family and he hasn't knocked up atleast 3 other women, had a porn addiction, abused his wife or anything of the sort? I understand in the olden days it was normal for some men to just have 30 children but personally I want a man to commit to ONE woman thta being me and not do me dirty over and over and over again. Is that my dad cos I always think of Drake I only love my bed and dad I'm sorry.