I hope this will help somewhat and that you have a good weekend.

It is difficult to speak for all of humanity across all continents and all of time. So I won't attempt that, but I would be surprised if the humans' need for love didn't exist somewhere. I am not a medieval expert and bear in mind, medieval western still covers a lot of countries with different cultures and a long time.

I can speak for my era of expertise, ancient (190-280 CE) China. Not a society that I think anyone would describe as capitalist with merchants looked down upon. Marriages were, for the most part, political in terms of connecting one's family with another useful family though also a way of furthering the family line (of course) and patronage. There was also concubinage.

Romance

So in the sources of this time, we don't get much on relations within marriages. It was a private matter and the records were not always interested in highlighting females even when they were major political players. One also needs to be aware, as Rafe De Crespigny puts it in Women of Later Han: Ideals and Reality

Despite the plethora of instructions to women about duty, responsibility and humility, we may assume that many husbands and wives had true affection for one another. Calm contentment, however, is unlikely to gain the attention of a historian,

before talking about what we do get.

Despite the limits of our records of the time, we do have love come through. I have written beforeabout the philosopher Xun Can and his love for his wife Lady Cao. Pang Lin and Lady Xi were separated for fifteen years by civil war but remained loyal to each other, the general Xiahou Shang was greatly distressed at the execution of his concubine to the point he tried to have her dug up so he could see her again. Emperor Ling wrote poems after his beloved Lady Wang died shortly after giving birth (and possibly murdered) in 181, when his eldest son (via different lady) the deposed Emperor Liu Bian was to be poisoned he asked a weeping Tang Ji to dance for him one last time. It was certainly not unknown for a concubine or a wife of an Emperor to be noted, for a time, to be greatly favoured. When the Wu prince Sun He was ordered to die as a former candidate to rule, his concubine Lady Zhang said "we should share bad fortune as well as good: I'll not live out of my life alone!" and joined him. The founding Emperor Sun Quan tried to force his court to accept Lady Bu as his chief wife but was blocked so refused to choose a founding Empress for a decade and when she died, forced the title posthumously. In the edict to mark this, he spoke of her help, sharing his labours, her kindness, his grief, ending with (translation Robert Cutter)

If her soul is still able to apprehend, may she rejoice in this favour and glory. Alas, my grief!"

Poets like Cao Zhi (Cao Rui's uncle) and Ruan Ji wrote of love in poems, about a man who had lost his chance to be with the woman he loved, wives either spurned or waiting to be united with their loved ones, playing on past tales of love. Works of fiction that followed the era including ghost stories would contain live: the court based scholarly tales of New Account of the Tales of the World, the Ming era tales of the fictional Guan Suo who wins one wife via a duel. The Records in Plain Language and the novel Romance of the Three Kingdoms were all able to draw upon themes of love.

As I touched upon in my Xun Can post, the fictional works (in non-capitalist China) added their own romances that have become famous. Turning Lu Bu's guilty affair with a handmaiden into a grand romance with a fictional figure Diao Chan, sometimes as a handmaid and sometimes as a wife who has been separated. Their romance leads to his killing his master and with Lu Bu portrayed as a man too emotional, lacking restraint, his feelings towards his loved ones helps doom him. Fiction turns the unhappy marriage between warlord Liu Bei and the fiery Lady Sun, who he feared as a spy, into a love match where she helps him escape the plots of her family.

It isn't just that people lived and loved but poets and authors wrote about it. Not always with approval, sometimes warning (as with Xun Can and Lu Bu) about lack of restraint does not end well. However, if the idea of love didn't exist then why do we have such tales and poems that people thought up and (correctly) thought people would want to hear?

If the lives of people of the time don't give you glimpses into married life (via mourning, loyalty and so on), look at poetry and fiction of the time, what they are doing and what they think people want to hear. If they talk about love and use it as a theme, it rather suggests the idea existed.

Daughters

This one there is even less detail on. Parents treating their kids perfectly nicely is, along with "eats food" or "content marriage", not something that the records of the three kingdoms would bother with. It was a private, not a state matter and the norms aren't worth recording. It is entirely possible to read about a figure of the era with the impression they never ate and only discovered they were married because they had children which only get mentioned on their death to explain what happened to their line.

Displays of filial piety as a sign of their proper behaviour or a bit of propaganda we do get. Sometimes when a powerful male had a powerful son, we did get glimpses of the life between father and son. With females sidelined in the records, treatment of daughters (who might often not be named) was not a priority in the texts.

In terms of the economic calculations of having a daughter as a long term tactical plan, as De Crespigny mentions when discussing the problem with infanticide

At every level of society and particularly among the poor, a boy was better: he would maintain the lineage, serve the ancestors and support his parents in their old age. A daughter could be a misfortune: a drain on family resources; of short-term value about the home; and a charge in the future when money was required for her marriage – after which she joined another household and was no further use to her original family. With limited resources in a subsistence economy, any female infant was at risk.

Even, say, a rich landowner with the resources not to worry about that, a child is expensive. They need clothing, food, education before the daughter needs a dowry. That is even if she lives that long: infant mortality was such that mourning rites weren't carried out for anyone who died too young. A daughter lives long enough to come of age and you have the money ready for her marriage? Well, there is the risk the marriage will be one not of your choosing due to violence/threats of or harem selection. Get her married off? If she ends up divorced (by his or her choice) or she doesn't have kids and is a widow then she could be back in the hands of her parents. Then there is always the "problem" of daughters having a mind of their own.

So as a political/social investment, a daughter wasn't an entirely reliable one while being expensive given long years of care required. Meanwhile, in over a decade they would spend at home, even if one believes that the parents are just calculating the long term, that is a long time where father and mother would be relaxing in their inner apartments, watching their children growing up, taking care of them. A lot of time for the same emotional pull, the parental and maternal love, that many parents feel now.

We do get some glimpses. Zhuge Ke, in a game of wits with the Crown Prince Sun Deng, drew upon a mother and daughter's love being so strong to defend the ear-piercing of an ox, if mothers could do that to their daughters then it was no crime to do it an ox. Guo Huai as a tactic for winning support among tribal leaders would ensure he knew the children's ages and how many they had. When the soldier Dou Li went missing and family was to be made slaves due to the belief he had deserted, the wife Ying argued his care for his children meant he would not abandon them (the matter was investigated and Dou Li was found to have been murdered). None of this would work without the idea that the parents loved their daughters (I specifically went with ones that were not just about the sons) and their sons.

There is another that often springs to mind. In 236, Cao Shu, the favourite daughter of the second Wei Emperor Cao Rui died when she was just a baby. Cao Rui was devastated and his reaction worried ministers (their protests are the reason we know of her death). He built a temple, ordered his officials to go into mourning and was prepared to leave his capital to go to the funeral which created chaos and would have been at some cost.

If Cao Rui had been mourning a political match that would have to wait for at least another decade to come into being, this reaction of his makes no sense. What he was doing was expensive, it annoyed figures at court due to the expense, confusion and a feeling it wasn't appropriate. There was no political, social or economic gain for Cao Rui in doing all this. It simply is that just that he had lost a child he loved and he wanted to honour her, to mourn her himself.

So yes, in the past, there was love. Marriages may, often, have been political and the power in relations was often unbalanced, life could be cruel to a woman. But the concept of love was in poetry and stories they told while, despite the urges of restraint, the reaction and loyalty of the spouses and the parents show us love that can be recognized today.

Edit: Added link to Xun Can writing