I've seen some interview with married women a while ago. Most did not like it, but expressed knowing that it might happen or might be happening and there's not much they may do about it. One was super against it and said she would leave her husband right away if that was going on.

I think the obvious answer is no it is not ok. But, will you actually do something about your cheating partner depends on so many things (as it does in any other culture) - whether you have kids together, if you are financially independent and can survive fine without them, how much you're willing to forgive etc...

This is probably different for gf / bf material though, or so it seems. To that I cannot comment at all.