I don't know how to explain it but wanting to know how a piece of media ends because of something like "I only think the one guy is hot and if she ends up with the other one I don't care" is very different than "I need to know how this piece of media ends in order to engage with it alongside you because the themes being presented in the beginning of the movie bring up a lot of complex and harmful emotions for me that I don't currently have the capacity to process in a healthy way" are very very different things...
There's a huge difference between someone just not liking the details or the suspense of the story, and someone who's worried about how those details and suspense will negatively affect them (during a difficult time, or otherwise).
If someone is asking you to "spoil" the ending of a piece of media you've consumed before because that ending might hurt them in some way, it's not wrong or ruining the fun to explain it to them- you're preventing them from harm. Consider why someone may be asking for the details of a story they've never seen before, or just ask, because otherwise that person is either going to have to (fairly) upset you by walking away from the content or by having to spend days after completing/interacting with it processing complex and painful emotions- both of which could just be prevented by telling someone how it ends.
