I have cheated and it's not something I'm proud of. On two different guys. I was also in a different headspace than I am now, and I'm not saying that it's justified, but it's not the person I am today. One of the times I cheated it was purely my fault - I was drunk off my face, and I just didn't care enough *not* to have sex. The other guy was... well, by that time it was a long distance relationship, and whilst I regret it, I do believe that cheating in a long distance relationship is a different mindset etc to cheating in your average relationship. Again, not that I'm justifying myself, but no one in here seems to have done it - or to be willing to own up to it - so I thought I would give you the perspective from the "other side".
And tatoodguy, I don't think it's fair to say that people are "weak" if they take back a cheater. My mum has taken back my dad in the past, and while at the moment I think she should dump him, it's not as simple as an adolescent relationship. For one, she has three children who she simply doesn't want being put through a divorce. Secondly, she knows in the event of a separation I will utterly refuse to live with my father, and she doesn't want to disrupt my HSC. Thirdly, there are a lot of assets they've gotten while they've been together - the house, the business, the farms - that she wants to be for my brother, my sister and I. She doesn't want to risk that some random woman and her kids can end up getting things that my parents worked for so that *we* could have them. There are other reasons why she hasn't left him yet, but I hope you realise that it's not just a matter of her being "weak".