Actually, I think cheating is less tolerated now than, say, 50 years ago. Once upon a time divorce carried a really nasty social stigma, the dutiful wife was expected to serve her husband, and if her husband should stray, well, "men will be men" and she should have simply served his needs better (with a societal double standard that a woman who cheats is a harlot and her husband has every right to divorce her). As such, many could cheat with fewer repercussions than cheaters today might encounter.
Personally, I know that if I ever caught my husband cheating I'd be liable to completely remove certain private parts with a rusty spork, and nearly every woman I know feels the same -- and most men I know too, though not in those exact terms. Maybe there are more people that will tolerate cheating, but personally I think that it's just not hidden as much as it used to be -- now if someone cheats it reflects badly on the cheater, not on his/her significant other.