Once in a while I come across a comic strip produced by a married couple. And I always think the same thing: "Your marriage and/or comic strip is doomed." That's because there's nothing harder to make than comedy. It will not abide politeness. Every single joke needs to be torn apart ruthlessly. When your writing partner shows you his or her best joke, lovingly conceived, birthed and grown to fruition, you need to be able to say "that is simply the most unfunny thing that's ever been." Because it's the truth. I'm not saying marriages can't stand a little truth telling. Mine certainly can, and does. But most can't abide the frequency and amplitude of truth necessary to write comedy. Something's gotta give. And so it will either be the comic strip or the marriage.
I'm sure there is the rare exception, and I bet you are one heck of a couple. As for the rest of you, if you insist on working with one another take my advice and go into toxic waste disposal or bounty hunting or something. It'll be easier on your marriage.