They turned out to be congenial to each other.
They are sympathizing with each other.
They like each other.
We are close friends, well used to each other's ways.
They are always gibing each other.
They clicked with each other.
They're very thick together.
They enjoy one another's company.
They are a well‐matched [an ill‐matched] couple.
They think about each other a lot.
They are a nice couple; they are always in sympathy with each other.
They admire each other.
They're related to each other.
They faced each other.
Those exist with each other in harmony.
They have mutual respect.
They are on good terms with each other.
They resemble each other in all respects.
I know they are in love with each other.
I know that they're in love with each other.
I know they're in love with each other.
I know they are in love with each other.