Why are MOST men cheaters? answer for me guys please!!?

so scenario for you... You've been with a girl for 7 years, your practically married, you love her so you say, she treats you like gold ,would do anything in her power for you. She's about an 8-9, would try pretty much whatever in the bedroom. She appreciates you very much and tells you on a daily that she loves you. And then you cheat!!!! why'd you do it??