Love

Love was an emotion which K9 Mark 2 struggled to understand, receiving no clear answer when asking his human company. (TV: Aeolian) In French, it was known as "amour". (PROSE: Going Once, Going Twice) When questioned by Brenna, Ian Chesterton defined love as a deep care for a particular person, coupled with an urge to spend all one's time with them. (AUDIO: The Invention of Death) Peri Brown defined it to Yrcanos, the man who would become her husband, (TV: The Ultimate Foe) as "when you care for someone or something more than yourself", "sometimes more than life." (TV: Mindwarp) Victoria Waterfield told the Masters of Space and Time that love was the most powerful force of all. (PROSE: Mastermind of Space)

According to the Twelfth Doctor, love was not an emotion, but a promise; (TV: Death in Heaven) Auteur went further and defined love to the Spirekeepers Mother and Father as "a promise to dare". (PROSE: Going Once, Going Twice)

The Tenth Doctor was confused as to how humans fell in love so quickly before he decided that it must be their short lifespans. (AUDIO: Death and the Queen) He claimed that love was stronger than Baboolian steel. (COMIC: The Parrian Proposal) Charley Pollard insisted that love would persist beyond one's lifespan. (AUDIO: Neverland)

Barbara Wright believed that love and loss, in the form of heartbreak, were "both aspects of the same thing". In large part due to the finality of death, heartbreak was inevitable. (AUDIO: The Invention of Death)

As Ian and Barbara explained, there were "different sorts of love". One might have love for a friend, for family, or for a romantic partner; each was expressed in a different way. (AUDIO: The Invention of Death) For instance, Yasmin Khan and her nani Umbreen declared that they loved each other, (TV: Demons of the Punjab) and siblings Eve and Durkas Cicero confessed their love for one another shortly before Eve's death. (TV: The Tsuranga Conundrum) Ryan Sinclair once expressed his familial love for Graham O'Brien, his step-grandad, though he wasn't willing to say it twice. (TV: The Battle of Ranskoor Av Kolos) Charley Pollard and the Eighth Doctor expressed their love for one another as friends. (AUDIO: Neverland)

In its most amplified form, romantic love could turn to lust. (PROSE: Slow Decay)

According to the Empress of the Racnoss, love could make people act against their nature, against reason. She found that it was a corruptive force, as it made people forgive others when they ought not to. (AUDIO: Empire of the Racnoss)

In his youth, the First Doctor authored a treatise on the chromosomal origins of love for which he received a "rubbish" grade with his tutor stating he'd missed the point entirely. (AUDIO: The Wormery) At the end of his life, the First Doctor noted love as an example of emotions to the CyberMondan leader Krail, along with hate, pride and fear. He questioned, "Have you no emotions, sir?" (TV: The Tenth Planet, Twice Upon a Time)

During Rory Williams's time guarding the Pandorica, Anna (AUDIO: I, Rorius) and Lancelot had both fallen in love with him but both ultimately recognised that he loved another. (AUDIO: The Last King of Camelot) A piece of art in the Big Brother House featured pink text reading "LOVE" above a yellow heart. (TV: Bad Wolf)

Mickey Smith loved Rose Tyler. (PROSE: Alien landing confirmed, etc.)

The Doctor
When asked if he had ever loved another, the Fifth Doctor answered in the affirmative, that he "[knew] what it mean[t] to have cared for people". (AUDIO: Empire of the Racnoss)

Although River Song once declared her belief that the Doctor was incapable of a romantic relationship, (TV: The Husbands of River Song) they proved themselves capable, on occasion, of expressing romantic feelings for others.

When with the Aztecs, the First Doctor accidentally got engaged to a woman called Cameca, when she poured cocoa beans in front of him, not realising the Aztec symbolism that sharing cocoa was a proposal of marriage. Cameca gave him a brooch during his visit, which he was planning to leave behind before leaving in the TARDIS, but then picked up again, indicating that he did show real affection for Cameca. (TV: The Aztecs) The Tenth Doctor later recalled still being on amiable terms with Cameca, having visited her on several occasions. (COMIC: Revolutions of Terror)

When speaking to Cindy Wu about romances, Sarah Jane Smith confessed to have fallen in love with "a lovely, brave silly man once" but noted that by the time she'd worked out her feelings, her chance had passed. (COMIC: Vortex Butterflies)

The Sixth Doctor once confessed that be believed he was falling in love with Bianca, an evil future incarnation of Iris Wildthyme, though these feelings were ultimately a ploy by the Doctor to defeat her, as well as an effect of the psychic worms in the alcohol Bianca had given the Doctor. (AUDIO: The Wormery)

The Seventh Doctor once stated that he maintained an external image of asexuality so as to keep his relationships with others simple. (PROSE: Death and Diplomacy)

Upon his regeneration into his eighth incarnation, the Doctor began to explore the realms of romantic connections with others, quickly sharing a kiss with Grace Holloway. (TV: Doctor Who) After travelling with the Eighth Doctor for several weeks, Charley Pollard realised that she'd fallen in love with him. (AUDIO: Letting Go) She confessed these feelings to the Doctor when she felt she was going to die, (AUDIO: Neverland) and the Doctor confessed that he loved her as well. The Doctor admitted that this was the first time in all his journeys that he had come to truly love a friend. He explained that all he wanted was to keep her safe, even at the expense of his own life. (AUDIO: Scherzo)

In one instance, a Dalek exploited the Ninth Doctor's feelings towards Rose Tyler, to make him compliant, by asking, "What use are emotions if you cannot save the woman you love?" (TV: Dalek) Some believed the two were romantically involved. (TV: Aliens of London, Father's Day, PROSE: The Beast of Babylon) The Doctor also told Rose that he found marrying for love overrated, saying she could "ask Lady Mary Wortley Montagu" to verify his claim. (PROSE: Only Human)

The Tenth Doctor had a number of female admirers, including Queen Elizabeth I, to whom he got married and left behind at the altar. (TV: The Day of the Doctor) When saying goodbye to the Doctor, Rose admitted that she loved him, but the Doctor's transmission to Rose was cut off before he could return the words. (TV: Doomsday) Martha Jones admitted that she loved the Tenth Doctor, but believed that he could not return the feeling because of falling in love never occurring to him, (TV: Human Nature/The Family of Blood) causing her to leave later on. (TV: Last of the Time Lords) In contrast, when the Tenth Doctor told Donna Noble that he didn't want a "mating" relationship with her, Donna remarked likewise. (TV: Partners in Crime)

The Eleventh Doctor grew angry that the Kovarian Chapter tried to get to him through the people that he loved, namely Amy Pond and her daughter. (TV: A Good Man Goes to War)

Hearing about the Doctor when she was growing up, River Song fell in love with him. (TV: Let's Kill Hitler) Though the two eventually wed, (TV: The Wedding of River Song) the fact that the wedding took place in collapsing timeline and lacked the usual amenities, such as a wedding cake or champagne, left River with deep insecurities about the whole affair. (AUDIO: R&J) While River made no secret of her love for the Doctor, she eventually concluded that he did not love her back before he dissuaded her of that notion. (TV: The Husbands of River Song)

In her final adventure with the Eleventh Doctor, Clara Oswald, under the influence of a Truth Field, admitted that she fancied the Doctor, and he himself was quite eager at the prospect of being her boyfriend, (TV: The Time of the Doctor) only for their relationship to briefly become more platonic when he changed into the older looking Twelfth Doctor. (TV: Deep Breath)

Despite this shift, the Twelfth Doctor frequently claimed that he had a "duty of care" for Clara, (TV: Dark Water) before later admitting that this attitude had been a knee-jerk response to her initial reaction to his regeneration and that he'd been in love with her ever since they first met, to the point of willingly subjecting himself to 4.5 billion years of torture as a gambit to try and save her life. (TV: Face the Raven, Heaven Sent, Hell Bent) The author of the Time Lord Academy textbook on Gallifreyan history believed that the Doctor and Clara's love for one another was the Hybrid of legend, noting that it perfectly fit the prophecy. (PROSE: A Brief History of Time Lords)

As observed by Dan Lewis, Yasmin Khan shared a mutual attraction with the Thirteenth Doctor. (TV: Eve of the Daleks) When Yaz brought this up, the Doctor deliberately chose not to act on these feelings, jaded by all the love interests she had outlived. (TV: Legend of the Sea Devils)

Other references
Singing The Riddle Song, Bliss recited the line "I gave my love a chicken, it had no bone. I gave my love a cherry, it had no stone." (TV: Love & Monsters, PROSE: The Time Traveller's Almanac)