Love and suffering is a match made in heaven. Love is breathlessly heart-wrenching, as it snares the mind of the lover and controls his actions. Any loving relationship will be filled with trial and tribulation, selfless sacrifice, selfish protectiveness, and frequent heartbreak. We both live and die for even a moment of true love. It is thus no coincidence that suffering is a component of many Arabic words for love. `Ishq (عشق), which is a fervent type of love, was originally a vine that winds itself around a tree, squeezing it until it withered. Shaghaf (شغف), which was the passion that Zulaykha had for Yusuf (12:3), was a form of heart disease. Muhjata qalb (مهجة قلب), an expression used to describe a lover, is actually the blood of the heart. Huyum (الهيوم), meaning passion, is a type of insanity. The Persian poem of Layla and Majnun comes to mind.
Most of the Quran is relative-comparative. Its stories usually lack names, dates, places, and chronologies, and are instead filled with archetypal symbols that can be flexibly applied to other situations. It tries to tell the stories in a timeless and universal manner.
The Husayni tragedy in Shii literature is similar. It is mourned by other prophets long before the event, it is mourned by nature (blood rain, blood earth, owls), it is mourned over by millions of angels, and it will be vindicated in the eschatological narrative. Karbala is described in Kamil al-Ziyarat as a piece of heaven on Earth, and as the conduit between heaven and earth (majma` as-samawati wal ard). Its soil is described as a cure, and it is given to the sick, and it is used for prostrations. In Shiism, the visitation of Husayn by one who correctly recognizes his status is considered a Hajj (or seven Hajj, or thousands of Hajj, or more), because the principle of Hajj is total submission and sacrifice, commemorating the sacrifice of Abraham; and Husayn cut his Hajj short to fulfill its end by going to Karbala and willingly giving himself to God. It is said that every grief in Islam is disliked, except for grief over Husayn, and so people forego their personal tragedies to mourn for the primordial epic tragedy. They wear black, abstain from makeup and dye, abstain from laughing, abstain from weddings and festive activities, sometimes for forty days.
The love of Husayn is not just lip-service. It is the intense gallantry that a mother has over her child, the undying loyalty that a person has for their spouse, the forsaken mourning of a widow, and the adoration of a boy for his father. It is a bond closer than family and thicker than blood. His tragedy is the quintessential love story, with Abu Fadl al-`Abbas, Qasim b. al-Hasan, `Ali al-Akbar, `Ali al-Asghar, Habib b. Muthahir, and many other gems bravely followed their beloved into the engulfing abyss.
Interestingly, there is no record of a relationship between the Imams and the historians of the tragedy, but there is much record of a relationship between the Imams and the poets. The Imams would invite poets to speak on the tragedy, make many supplications for them, add to their poetry, and gift them very generously. This to me says that the aim of the Shii is to find a meaningful and meta-historical route to Husayn, as the horrors of that day were unfathomable, and directed only at those who deserved it the least.
Love and suffering are often paired in Islamic literature. There isn't really a concept of "happily ever after" in this world, it is rather seen as a prison of the believer, an abode of trials (dar al-bala'), a fleeting world (dar al-fana'), where the lovers of Ali will suffer the most, so that they may be refined and purified like gold in a furnace. The tradition says that those who suffer the most are the prophets and their successors, then those similar to them, and so on. The constant trial strengthens the faith of a true believer, who learns to lean on God alone.
The timelessness of Islam's symbols emphasizes the finality of its message and the universality of its principles. Our religion uses relatable similitudes that resonate with our very core, making Islam not a seventh century Arabian phenomenon, but an expression of the nature in which we were created.