You can get stale writing with each other for a while.
You're going to have more rejection than acceptance.
I know at the beginning of our careers, my wife and I were gut wrenchingly competitive.
You have certain writing tools but generally creating something from nothing makes one quite mad and Cynthia and I are quite mad you know.
You've got to really be able to accept the rejection.
I think if one wants to be in a continual state of insanity one should stay married to that writing partner.