Yes, I didn't bother to mention the exceptions, because this person is either a cheater or a cheater apologist and simply won't listen to reason, logic and facts, they will just keep twisting it.
But yeah, there are loads of really good reasons I can think of off the top of my head why someone can't have/won't want to have sex. Pregnancy, childbirth, cancer, death of a child or loved one, having to go and help a family member in distress, all kinds of illnesses. There are LOADS of reasons why sex can dry up that do not make the person not having sex unfair or unreasonable.
And since everybody has a different sex drive if you allow the excuse of "but you wouldn't have sex with me!" with the pouty bottom lip, that means filthy, grubby cheaters have a get out of jail free card at any time at all - some would claim two weeks is too long to go without. There are men who are coercing their wives to have sex two weeks after a baby is born.
So the bottom line is no, there is no time limit at all that is an excuse for cheating.
I also love that the cheater/cheater apologist I replied to seem so oblivious to the fact that often women stop having sex with their husbands BECAUSE he was cheating on her while they were still having sex. Or, because her husband was otherwise abusing her and treating her like garbage.
So yeah, a man can abuse the hell out of you, treat you like garbage, but then if you don't want sex with him somehow he gets a free cheat pass as well.
It's just this simple - when you agree to monogamy, that's it. You don't get to have sex with anyone else, ever again. Forever. No matter what. And if you no longer agree to that jointly established boundary that you made through choice, you tell your spouse and discuss it and change the rules jointly, or you leave, or you tell them and they say no and then you leave.
And anything else is cheating and makes you the bad guy.