when a man/woman cheats is it because he/she is not happy at home

Happiness and being fulfilled in your relationship are 2 different things. I do NOT support cheating what-so-ever- so I believe that if you are not in a fulfilling marriage and feel the need to stray, that you are not communicating with your partner enough to get those things that it is you NEED out of your relationship in order to NOT cheat. So, my answer to your question is that NO, i dont think it is because they are not happy, I think it is because they can not communicate effectively.