I spose it all depends on how you feel about sex, how you feel about your partner, and in a lot of ways how you were brought up, religious stance, the list is probably endless. Most couples seem to go along with the one partner sex rule, although there are some for whom having multiple partners is fine and works for them
It's all down to personal preference, for example, when married I would never have considered sex with anyone apart from my hubby, now the reasons for that would probably a lot to do with "it's just not expected or acceptable" and I had no inclination to do so... when divorced then sex became just that sex so therefore I wasn't as restricted shall we say.
Now I am in a full time relationship again I feel it's not something I think about or would want to do.
So really in answer to your questions I believe it's really all down to personal choice
It's all down to personal preference, for example, when married I would never have considered sex with anyone apart from my hubby, now the reasons for that would probably a lot to do with "it's just not expected or acceptable" and I had no inclination to do so... when divorced then sex became just that sex so therefore I wasn't as restricted shall we say.
Now I am in a full time relationship again I feel it's not something I think about or would want to do.
So really in answer to your questions I believe it's really all down to personal choice