I have to disagree, and actually have a story. I have a long story with my GF. We dated 3 months, the 8 months, then one year. However, I cheated on her, once, (not an affair) on the first two months of our last year together. I can´t explain how that happened and actually i feel very bad. I just told her a couple of months ago, and we are apart for the time being (while she decides if we are to continue together). I have never cheated on her before, nor have a cheated on her after that stupid mistake, and definitely I wouldn´t cheat on her after that mistake (if she takes me back of course I think that to say if someone who cheated will always cheat it is necessary to see the reason of the infidelity. If the person who committed the infidelity is a "thrill-seeker" i think he/she will always be a cheater. I know I won´t.