I think it's all too easy to judge other people for cheating. Some people will have their reasons and other will do it just because they're daft. Please don't think I condone it but it's not always straight forward.
I have been cheated on once, maybe twice and I have also cheated on someone. It was a bit tit for tat, he did it to me so I did it to him and then left. Silly, but I was young and wanted to get him back. I don't regret it as such but with hindsight I would rather not have hurt him and it was very childish, I should have just said my piece then left. I lost friends over it because of their strong opinions.
I have also been guilty of finding the next person before I leave the one I'm not happy with, but in that case have finished the current relationship before moving on.
I don't like the tag of once a cheat always a cheat, I think it's unfair to put that on everyone when you don't know what goes on in a relationship. I'm not saying it doesn't happen that way, I'm sure there are people who are serial cheats and will never change. Like I said, I have done it once as has the man I am with now and I am certain I would never cheat again because of the damage and hurt it causes, not only to the couple but it can also divide friends and family.
I trust my boyfriend totally. We are very honest with each other and are the best of friends and I think if there is any doubt on trust it just causes torment and unhappiness. I do resent that people who don't know me or anything about the relationship I was in at the time would label me a cheat. Yes I have done it, no it wasn't right but that doesn't mean I'm going to do it again.
Having been on both sides I can say that I would not stay in a relationship if I was cheated on again and if I ever did it to someone else (which I know I won't) I also would not stay because if you really wanted to be with someone surely you wouldn't have done that?