So I have a story...
Story in a nutshell: A gay boy gets kicked out of his mom's house, he attempts to commit suicide, but doesn't. Next his best friend Roseline starts dating Shermen, his other best friend. Then his lung cancer redevelops, but before he dies he gives his friends his blessing to get married. And then, he dies.
Note: I would like a one word title.
LOL.
I honestly hope, you aren't being serious.
Hmmm... I don't know. It's indeed a little bit too dry compare with the seriously style of the whole story. But it's one word.
I'm not going to read the stories because I'm not a fan of stories where one of the main characters dies... Sorry, just not my thing... But, from your short description of the overall plot a few things came to mind:
Terms This could be relating to terminal cancer, coming to terms with death, and/or the gay character coming to terms with himself and/or his friend's relationship Earnest It's a word meaning both "very enthusiastic" and "serious; very important". The first definition is related to gay (i.e. "happy") in round-about way. The second definition could relate to all things listed above for Terms. Absolution, Mercy, and Pardon could also possibly relate to your story.
I don't know if any of those would fit what you are looking for but I hope you find my suggestions helpful somehow or another. :)
Also, for single word story titles, I sometimes use this off-site Thesaurus website (Click me!) to search words relating to the story until I find something that fits.
A one word title... rams head against a dictionary.
Maybe Morbid? It is a word which is connected with suicide as people who are suicidal are said to be sullen, and morbid is a synonym. Meanwhile morbid also means inspiring disgust or horror (homophobic mother), and also in the field of medicine as one of the online dictionaries mention - relating to or resulting in illness (so I think it correlates with cancer)
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