Simple logic to live by ...
There are fairly simple and straight-forward logic that I live by after fifteen years with the same woman ...
First off, it's not "the 'D' bomb." I.e., don't use it like a "F" bomb as if it's of some great use for "shock value." Nothing pissed me off more than when my wife used it a little too loosely many years ago. You only start saying it when you really mean it, and never in anger. My wife learned that lesson when, the last time she ever used it, I calmly dropped my emotions and started planning it. Not to "teach her a lesson," but to get her to realize, "okay, here's what I expect, now what are you looking for?" She has never done it since (for many years now).
Secondly, relationships (however they are defined) are about sharing, caring and tenderness. If those aren't there, then the relationship may have issues. If the communication lanes are honest and open, they may be worked through. The result of that communication may be resolution or it may be divorce, but you must find a way to come to it without emotions. Otherwise the emotional issues are only going to continue on post-divorce, although at least you're not living with the person any more -- but kids can complicate that (so you almost are).
If you follow that logic, then you're likely going to make rational decisions that benefit your relationship, instead of harming it -- and may includes if and when the relationship comes to an end, as a benefit for both. There's no contest or award for being with someone the longest. There is no arbitrary or absolute equation that says things are right or wrong. Relationships are about exchanging values, finding contentness and finding happiness. If people aren't focusing on that, and focusing on other things, then communication is the problem. And people do change over time, and not all changes are compatible.
Of course, sometimes one party is not mature. Or people aren't ready for relationships. I don't know what to tell you, that's far more difficult to deal with. I met my wife at age 20 and her at 18 and we've been fucking like bunnies since then. Everyone said we'd fail, were totally against us being together and that continues until we married, and even for several years after that. Finally, one day, the bullshit from other people stopped. But the funny thing is that it never defined us, so it never affected us.
That's what matters most.
-PV
Additionally, and I wanted to make this separate because most people will really differ with me on this ...
I don't believe in make-up sex, at least for myself. I don't believe in basing my relationship on extreme, roller-coaster love-hate or, more accurately, love-after-dislike. If people are basing their relationship on such emotional extremes, then either they have some sort of maturity that exists on a higher plane that most can't handle (including myself and my wife) or, far more often, they are hurting each other and using sex to look past it. It's no different than alcohol or drugs or eating when upset or shopping when worried, etc... Heck, I don't even sleep with her after she's been drinking. A lot of women -- and I mean a lot of women did not like me -- because of this, and even my wife (when she first met me) questioned it.
Understand, to me, make up sex and putting aside troubling emotions to bring temporary happiness are a major issue. While the religious right preaches no sex before marriage, what they should really be is preaching the real issue -- couples who have sex to avoid conflicts only to have issues after a few years (after they are married). I don't know how many times I've had that debate with religious people who say my life (both before and after marriage) was "wrong." They don't like it when I ask them if they've ever had make up sex, and then start using their own Bible against them on that (among other things, including self-righteousness).
Making love is important. Fucking like bunnies is fun. Nothing wrong with, even among new couples. I encourage people to fuck all they can, responsibly. If there was a way to introduce this concept and get people to deal with it at a secondary education level, without all the ethics and legal bullshit, I'd be all for it. It's a major part of a relationship and it should always be. No one should downplay that, ever, or label it is "bad" for the relationship, because that's bullshit. Controlling and dealing with one's emotions is the more important detail. Being honest and open and responsible with ones partner -- and not more arbitrary and absolutist concepts like divine, faithful or righteous -- is what matters most.