"However, if I changed my mind in the morning how do you prove I'd said it was ok the night before? Say I woke up in the morning and thought I wouldn't have looked at him twice in a saner moment? Or I was married and thought "oh my god what do I do now - oh I'll say he raped me".
In real life, he doesn't have to prove you said it was ok the night before. In real life, what would happen is the man would say 'she consented' and it would probably just about stop there unless you were sporting some obvious horrendous injuries to prove what a 'bad' rape it was.
In real life, hopefully, you wouldn't ever consider bringing a rape charge to cover up cheating on your husband.
In real life, hopefully, you wouldn't ever consider bringing a rape charge because you had consensual sex with someone you might not've in other circumstances.
In real life, hopefully, if you DID bring this rape charge, the police would ask the man why he felt you consented, and he would give examples of you initiating and/or happily engaging in sexual activity.
Whether or not you are married or regret sex is NOTHING to do with rape. It astounds me how many people seem confused by this point, and all I can think is that it's a wilful misunderstanding, honestly. Because I am no genius, and it has never, ever, seemed confusing to me.