Looking for an accurate expression (department: Romance)

[Nordic Bill]

What is the colloquial term for the stage a couple goes through once the initial excitement of the relationship begins to wear off, minor irritations occur, and they see a need to start adjusting to each other's differences to maintain harmony?

I have it narrowed down to these two, but I'm not sure if they are correct:

They’ve reached the stage where they are rubbing each other’s corners off.
They've reached the stage where they’re filing down each other’s rough edges.

Do either of these ring a bell? (I mean grammatically speaking, I'm not prying)!

[Mags]

No they sound too crude and raw . The first flush of excitement THEN friendship Then sometimes HABITUAL
I know what you mean as when you see "warts and all ", the excitement has gone , routine and familiarity takes over.
I woud use the word FAMILIAR or TOO familiar with each other .
When getting to know one another I would say adjusting to one another or "testing compatibility" or testing the water

[Curious Cat]

It can be also said that people learn to smooth things over, or start seeking for harmony in realtionships.

[Nordic Bill]

I think smooth things over would be more descriptive of settling an argument. Although smoothen things out might be on the right track.

Jeez, I knew this would be a tough one to pinpoint.

Thanks for your suggestion.

Bill

[Casiopea]

What about?

They've reached the end of the honeymoon stage.

[Mags]

Nice replies What about we should really talk about this (whatever the problem may be)