I don't know. I certainly don't. That is why its important to pick the right person.
"Why cant cheating be seen as a wake up call, instead of such a disaster? "
Because it destroys trust. And without trust, the relationship is not going to continue. A wake-up call is something your alarm clock does. Cheating is something your best friend/life partner/husband or wife does. The terms husband and wife mean things to many people. Of course, to other people, the terms are just words in a dictionary.