The problem Ironcross is that there are different levels of fighting.
I know a some couples who have relationships based entirely around sparring with each other, this can range from playful, to pointed, to down right nasty. No, resentments don't buidl up, but equally you get cases where patterns of just running into unpleasantness become ingrained and even comparatively normal disagreements get extreme, I once heard a police officer say he was called to a domestic disturbance in which a woman had clobbered ;her husband on the head with a baking tray during an arguement about whether Michael Jackson was or was not the king of pop .
Then you have the other side as you mention, where people tacitly ;accept faults and not disagree, indeed this can often lead to some pretty nasty domestic abuse situation where one partner is constantly accepting things from the other where they shouldnt' necessarily, and resentment builds, that of course when one partner isn't taking advantage in a rally unhealthy way.
You then however have the third kind, which my lady and I have where disagreements tend to get talked over and where any sparring we do tends to be more like verbal byplay than any sort of personal comments, actually it was quite funny that when we performed "I can do anything" on stage one teacher said we had to give it a little more punch for it to actually work.
Yes, we have days where everything goes wrong and we feel depressed or we end up shouting at computers, but since neither of us likes to argue we tend to resolve these sorts of things without getting personal since we're one of these cases where we could both do each other some serious emotional damage as we pretty much adore each other, heck we're even careful about sparring.
oh and yes, I will admit that we have probably one of those marriages which makes all the cliches come true, for all that we obviously both have our collected baggage.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)