as for 'cheating' relationships lasting...i know a LOT of them that stay together for a long time and even get married. yeah THAT'S fair and just....UH@ NOT! just saying...
I think in those situations there is actually some poetic justice there...first, they both KNOW they are with somebody who will cheat, so there will be some distrust of eachother right from the start, and they are both stuck with somebody who has some moral/ethical/personality faults...really I think in the long run, the person who didn't cheat comes out ahead and gets the best deal out of the whole mess every time. He/she is no longer with a cheater, and is free to find somebody who is trustworthy...just my take on it...