I agree with @Zibbidoo.
I'm finding it hard to articulate how but a lot of people seem to struggle with where a line has been crossed when it comes to sex and rape, just because so many people would be in this 'grey area' in their own relationships.
Are you consenting to sex when you're too tired because you (not your partner saying so) know you'll enjoy it when you get started?
Or are you only consenting to sex because your partner won't take no for an answer and it's easier just to get on with it?
Are you only consenting to sex because your partner is coercing or pressuring you to have sex (including them telling you that you'll enjoy it when you get started)?
Are you only consenting to sex because your partner isn't taking no for an answer?
Are you only consenting to sex because you can't take another argument about not having it?
Are you only consenting to sex because your partner will be angry or will sulk if you don't have sex?
Are you only consenting to sex because your partner will get violent if you don't?
Are you only consenting to sex because you've been indoctrinated to think it's your only purpose and you've been deliberately kept uneducated and raised in a society that values you for your breeding potential only and you know nothing else and you'll be killed if you refuse?
And are you only with that partner in the first place because you've had no choice but to marry them. Nobody asked you and if you complained you'd likely be killed as either a gender traitor or a traitor against the state?