I'm with quisath.

When you can no longer communicate with your partner I find that the next things to go are:

Trust
Fun (highly underrated within relationships)
Good Sex
Consideration for the other
Respect

I believe it all stems from communication.......as for what causes that to go....I dunno. Could be any number of things I suppose. But complacency is definitely something that would be high on my personal list of experience with this kind of thing.

__________________
"Time flies like an arrow -
Fruit flies like a banana"

M Y - N A U G H T Y - P I C T U R E S ! !