There seems to be two types of people who cheat... 1) ones that get caught in the moment and can"t help themselves, includes players. 2) Ones where the primary relationship isn't meeting their needs so they are forced to venture outside the relationship, includes people whose spouses may have refused to have sex with them for months or even years.
Because it felt right. Me and my boyfriend back then were going through a difficult time and we had gotten into a fight where he shut me out. I was on the edge of breaking up with him because the relationship was getting toxic so I went out with my girls one night then followed a super hot guy home and slept with him. I cuddled him while my boyfriend texted me. I broke up with him later on, that guy was not healthy. I wanted to feel loved and appreciated, I remember thinking that this one night stand gave me more "love" in one night than my ex ever did. I don't regret it, it made me see things clearly.
Yes - I cheated a few times on the same person.
Reasons: 1) I have a much higher sex drive than my partner (I'd like every day, whereas he seems happy with twice a month). 2) I had a career set back and my partner was being highly critical towards me at a time when I was depressed. 3) The more selfish reason -- I was not an attractive teenager but I am an attractive adult, so getting attention from men is always a bit of a novelty for me.