Relationship gone downhill. What can we do?

We used to have a good relationship but in the past 5 years it's gone downhill. Two years ago it had major issue and 8 months ago I started sleeping downstairs.

Now it's polite: "hello/goodbye/ Will you buy cat food "
I think about how it would be great if we liked each other for the family sake. We have two daughters in college. But the feeling can't be just magically conjured up.

When we had the major issue it seemed to come as a surprise to her and her friends because they said to her: oh we thought you had a good relationship.
To separate at my age scares me. I might lose the house (I can give her money). Being single etc
It's exciting too... Getting the feeling of love and attraction.
Relationship gone downhill. What can we do?
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