Hello, could you tell me which one is more natural to native English speakers,

"How this movie will end up?" and "How this movie will end?"

"I can not tell you how our relationship ended up" and "I can not tell you how our relationship ended"

So my question is whether I have to distinguish between usage of "end up" and "end" or not. Thank you all the time in advance.
Since you're asking for the most "natural", "end up" is not necessary.
However, your first question would feel more natural to me if it were worded thus:
"How will ( or How does) this movie end?"
How does this movie end? (Not end up).
I cannot tell you how our relationship ended. (Not ended up).

End means finish. End up is an idiom, which is used when you find yourself in a place or situation in which
you did not expect to be, e.g. She ended up in the hospital; he ended up doing that difficult task by himself, etc.