I know it's traditional to set up a dichotomy between logic and emotion, but I tend to think that, biologically speaking, emotions are completely logical.
I've got to disagree with you there. Emotions are rarely logical. They're based in the lizard-brain chemistry that managed to get us where we are today, and they're a vital part of our brains, but they exist on a lower level than the logic--the capability for logic is built upon that infrastructure.
That's not to say that emotions and logic have nothing to do with each other. I've read multiple SF stories recently that posited that for an AI to be truly functional, they have to be capable of emotions to help them weight their decisions, or they'd be paralyzed with all the tiny meaningless choices we make each day like "should I wear a red shirt or a blue one". The choice of a shirt might not have much emotion so can be done randomly or with little consideration in many situations, but deciding whether or not to do something else would be weighted more heavily if it has to do with maintaining your marriage, maintaining your health, etc. I don't necessarily buy into that argument fully, but I see its basis. I agree that an AI would need to have some kind of utility function that would help it weigh minor decisions vs vital ones, but I don't think that emotion need be the basis of it.
Emotions are something like biological shortcuts that get you to engage in certain helpful behaviors without the need to think through why, exactly, they're helpful, but they're undergirded with a distinct logic. The fight-or-flight response is a classic example. I'd argue that love is another one.
I think I agree with the basis for your argument on this, but not your conclusion. I can buy into emotions being biological shortcuts aimed toward certain helpful behaviors. Without the fight-or-flight response, our species would not have survived to this point. Without love, likewise (reproduction can happen without love, of course, but I think there's reasonable reason to think that multiple-parent childrearing encouraged by love as a motivation has an evolutionary benefit in harsh conditions). But that just means that
on a species level our characteristics have proved to be part of our evolutionary package that has allowed us to get to this point. That doesn't mean that these things always help with individual survival, and often drive an individual to states that are detrimental to that individual--death by hypertension caused by stress, someone cheating on their long-term lover and ending a marriage as a result, cravings for fatty food because that was a valuable trait when we were in the wild.
Anyway, I don't think that it's right to have a dichotomy between emotion and logic, because they are entangled in a way that at least in a human brain can't be disentangled. But I also don't think they are equivalent.
I'm just saying that any human lover engages in the exact same logic, only with an emotional shortcut that allows us to use romantic terms like "unconditional love" or "self-sacrifice" while ignoring the fact that treating each other according to the template of "love" carries with it a huge reward for the lover as well as the beloved.
Again I think I agree with some of your bases of argument but not your conclusion. I can see how you can say that human lovers might start a long-term relationship based on the logic of the benefit they will receive, and that's what Dae does here. So far so good. But then what drives some men to beat their wives? What drives some people to cheat on their spouses? What drives some people to kill themselves? It ain't logic (or it ain't OFTEN logic, I should say). Emotion can drive you to ends that are ones you might logically choose, but it can often drive you the opposite way as well down paths that destroy you or destroy those you love.
On the one hand, I might say that Dae would make a superior lover, because he is focused on the long-term end which she has already seen is to be with her a long long time, and won't be distracted by the emotional impulses we all have to contend with. On the other hand, I might also say that I'm less impressed with Dae's ability to do this for hundreds of years than I would be by any married person who managed it for 10 or 20 or 30 years because he lacks the biology that MAKES it hard. He doesn't have to struggle with ethics and morality and emotional impulses--he has decided this is the beneficial course for himself, and he follows through with it, end of story.