For what reason would you break a perfect relationship?

Let's say you are having the best relationship, everything is great and you both are happy ( over the clouds) , for what reason you might break things up!
I thought of a couple, but can you add more?
1- cheating.
2- Self destructive behaviour ( you think you don't deserve happiness).

Most people can't appreciate what they have, they don't know what gratitude is.
What do you think?
Have this ever happened to you?
Updates:
1 y
MHO again !
For what reason would you break a perfect relationship?
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