Roommates/Neighbors Yaoi

Runaway kid (he’s actually 20) gets picked up by a bad adult.
Trigger warning: alcoholism.

Gloomy Hitoshi finds a scary criminal Mah, who demands he let him live with him.

Friends lie and say they're a couple to live together, have to fake sex (immediately just default to actually having sex) to trick the landlords, also one of them is gay and already in love with the other.

Working adults and roommates are told they can't live together as friends, decide to get married instead.

Coworkers get married for various reasons, one of them is already in love with the other.

An arranged marriage between an office worker and a student to save the village from calamity, and now they have to live together until they do the deed.
No trigger warnings.

Ch.1-3 - Runaway at 3 AM - Two years ago, Takaoka's lover Yukihito left their home with only a note, and Takaoka didn't chase him. Now, a young man who claims to be Yukihito has appeared, though he's too young. It turns out he's Yukihito's younger brother, Naoto, and he gives Takaoka the push to find out why things ended between them two years ago. Ch.2 includes the story of Naoto and why he ran away from his lover, Ise, kicking off this whole thing.
No trigger warnings

An established couple living together.

Momo sells himself to get by until he meets Yata, a man who can’t help but take care of cute things. They build a relationship but Momo has a lot of trauma that he needs to unwillingly work through. They’re a very cute and believable couple and the story works through real issues in a meaningful way, so it’s worth a read.
Trigger warnings: noncon, rape, gangrape, statutory rape, child prostitution

Fuji loses his memory and has to try to figure out his relationship with a former classmate who is his current roommate who he thinks may be a porn star, but who is actually his boyfriend.