A few reasons why we cheat

Spouse is abusive, physical or emotional. Husbands can be jerks and wives can be bitches. We look to someone else for attention and affection. Which isn't a wise choice to do because then we get emotionally attached. Your lover may not feel the same and has no intentions of leaving their spouse. It's risky.

Others cheat for the lack of sex. Scarlett raises her hand "oh..oh..me..me!!"
The passion and desire isn't there anymore. The spark has slowly flickered away. The sex is okay but where is the foreplay? Multiple orgasms? Sex drive? Various sex positions? We try and encourage our spouse to try different things and they refuse. Other times we don't say anything because we want to spare their feelings.