"Men are only as faithful as their options"--- Chris Rock
It's got to be tough for a man in any scenario where he's semi-famous or famous, travels the world, and has women throwing themselves at him. Then you add to that the fact that some of these rappers grew up in places with very little diversity. All of a sudden they've got European b------s with blonde hair whispering s--- in their ear. You can only say "no" but so many times. Best thing to do is be single once you make it big or at least have your girl understand that there will be sidebitches.
As far as rappers saying "b----", it's probably a business decision more than anything else. They probably reconcile all of that by making sure that their daughters don't end up with dudes like them (assuming they're trying to be good fathers on some level).
