Help me find this BL manga, please!

I only remember 100% that it's a BL MANGA, NOT a manhwa/manhua, it had quite a big of an age gap but I'm pretty sure it wasn't a grooming/unhealthy relationship, I think they met when they're both of age and this one scene: the ML has an unhealthy habit (I think he either smokes or drinks, not sure) and the MC told him he should get rid of it so that they can live long together but the ML reminded him he'll probably die before him anyway because he was older and then the MC cried lmao

Also just in case someone recognises this GL one-shot manga as well, please let me know, I've been searching for it for a long ass time, here's what I remember of it:
- high school setting
- story centers around self-aware harem manga characters
- MC is the childhood friend of the harem protagonist and is the least popular love interest, FL is a girl who was supposed to debut in a post-apocalytic manga but accidentally ended up in the harem manga
- MC has blond shoulder-length hair and big breasts (plot relevant for some reason?), FL has black long hair and is sort of tomboyish
- the male character is ugly (like all harem protagonists smh) and has long side-burns which the FL makes fun of
- two important scenes that I remember: first is when the guy is supposed to enter the girls' locker room, but the FL locked the door, and the second is the last (I think?) scene; the FL, accepting the fact that she's stuck in a harem manga, tries to meet up with the male protagonist so that she can become another love interest, but the MC who developed a crush on her stops her physically, either by hugging her or kabedoning her, can't remember for sure

Sorry for the big ass block of text, also thank you in advance if you know either of these.