I've thought about this question, because I think XWW and I thought about our relationship differently. When I was married, I probably would have said that marital love was supposed to be unconditional. It was a commitment to this idea that was at least part of the reason I tried to reconcile with her. But that didn't last. I think most of the people here are forced to admit that there are some things that love cannot survive.
But there are other ways of thinking about this question. I think back often to a conversation that XWW would later point to as a justification for why she checked out of our marriage.
At the tail end of an argument (I don't remember what about), I had declared that I loved her, and she asked "Why? Why do you love me?"
My answer, "I love you because you're my wife."
This wasn't the answer she was looking for. She wanted me to list the things that I loved about her. But that wasn't the question she asked. To me, my love for her wasn't a matter of her having won me over with her wonderful qualities, but a part of the bond that we shared, and that we had build over a decade of knowing each other and sharing life together. To me, the answer of why I loved my wife was very much like the answer I would give to why I loved my daughter. Sure, I could list all the cool things about my kid that give me a since of pride and joy, but none of those are the reason that I love her. I love her because she's mine. Period.
I felt the same way about my spouse.
To her, the answer I gave to that question was disappointing. After all, she explained, there wasn't anything specific about her. My answer could have applied to anyone.
To me, it was exactly the opposite. What I had said was important precisely because it COULDN'T apply to anyone else. For any quality of hers I could name, there could be many thousands of others who shared it. But none of them were her. The thing that made her special to me was that she was special to me. To her, this was a bland and unromantic way of thinking about love. To me, it was the most meaningful way possible.
I think my way of thinking has been borne out somewhat by what happened. Ultimately, I was replaceable to her. Expendable. Able to be reduced to what she was able to get out of me. When she had an affair, she got whatever she was interest in out of me, and whatever else from her AP, and then discarded me. And that's something I never would have done to her.
I think this is what people mean when they talk about conditional vs. unconditional love. I don't think they mean that you have to forgive people for doing horrible things to you, or stay in a relationship that is harmful. I don't think it means that love is supposed to survive horrific brutalization from things like infidelity. Frankly, as far as conditions go, not betraying and abusing someone is a pretty damn low bar to clear, and pretty amazing that all of our spouses somehow failed to clear it.
But while I definitely discovered in the worst possible way that there were definitely things that could kill my love for her, there wasn't anything she had to do to earn it. I think that's what it supposed to mean. I don't think everyone really thinks about marriage in this way.