Apologies if the thread title seems “click bait-y”.
Of course, any sane moral person knows that “no” means no and should be respected. But established relationships are not black and white.
So this thread assumes, the relationship in question is reasonably healthy, and devoid of physical abuse.
When your SO initiates sex, and you say “no”, is that usually the end of it? Or does the other person try to do at least a little bit of convincing?
No one I’ve been in a relationship has ever been pushy if I’ve conveyed “I don’t want to right now”. The closest approximation has been if she thought I was play-acting reluctance. The possibility of play-acting reluctance is indeed, I think, a characteristic of an established relationship. (some folks even extend such a pretense to elaborate involunary scenes, but they usually have safe words established).
It all depends on the “no”. If it’s “No, we have to get up in 4 hours to leave, and we’re both plastered, so it probably won’t go well anyway”? Or “No, I don’t want to/don’t feel like it/hate you with every bone in my body right now”? Because in the first case, I can probably be convinced to give it the good ol’ college try. In the other, she knows better than to push it. The couch is damn comfortable, and I’m happy to sleep there for a few nights.
I had this come up recently, where at the beginning of the conversation I was like “nah, I don’t feel like it right now…” but by the end of things we’d worked ourselves up pretty good and everything we weren’t going to do, we did.
So the dude was really upset with himself afterwards for having proceeded when I’d said I didn’t want to, and I was like “but it turned out I did want to” and he still says he’s mad with himself and I’m like “don’t patronize me by thinking you took advantage of me when I assert that you didn’t and I made my own decision!”
Anyway, it’s fine and stuff but it makes me laugh that I guess this is life as a pair of feminists 
Sometimes there is persuading (say on the road from just cuddling to something more vigorous), but “I don’t want to” or "no’ is always respected. It happens that just being close lights a spark.