Don’t be a dick.
If you love the person you’re with, don’t treat them like shit. And if your excuse is that they’re treating you like shit, then you probably shouldn’t be in that relationship (okay, you definitely shouldn’t be in that relationship). It’s inevitable that when you’re spending so much time with one person, you’re going to take shit out on them and say things you don’t mean, but try not be a dick. It will only do damage.