This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Mummies Alive!
The ending of "Desert Chic" with Apep, a demon snake, falls in love with Nefer-Tina, and Nefer-Tina feels the same way! Only probelm is they are both on opposite sides. The final scene, with Apep saving Nefer-Tina as she fell off the bridge was rather endearing. A lot of things must have been going through his head, loving Nefer-Tina or getting his revenge, and in the end, he chose Nefer-Tina. Which makes the fact that he had to go back through the Western Gate anyway even more heartbreaking.
The whole story of 'Rath & Chontra' from "Good Bye Mr. Cheops". When Rath tries to admit that he did have strong feelings for her and that he was just afraid of what those feelings would do to him. At this point you'd think that Chontra might have a change of heart, or at the very least pause to contemplate his words. She instead laughs, telling him that the only reason he reciprocated her feelings at all was becuase she had placed a love spell on him, which he was later able to shake off. OUCH!
Just about everything the Mummies, especially Rath went through in "Eye of the Beholder".
Just about everything involving Ja-Kal's backstory. From never getting to see his kid grow up to his fractured relationship with his brother. Not to mention his nephew Kimas, who like him isn't into his father's hatred for his uncle, and pulls a Heel–Face Turnand a Heroic Sacrifice. Man, it sucks to be Ja-Kal.