I'm thinking of a Yandere Roommate who,
used to live in your house, without you knowing. He used to live there way before you, so he did not like it when you bought the house he was living at.
Yandere roommate who loved to spook you! The look on your face when you thought your new house was haunted was just too funny and maybe... a bit cute?
Yandere roommate who got absolutely furious at the stupid guy who does morning jogs in the street in front of your house, when he stopped to chat with you.
Yandere roommate who finally decided that it's time he made his presence known, there are a lot of people who wants to steal you away from him. He cant have that because then his life would become so boring!!
Yandere roommate who got so happy when you accepted him to stay with you, tho he did wonder why anyone would do that, he decided to ignore it. Afterall, you're the only one who showed him some semblance of acknowledgement.
Yandere roommate who used to be bullied and shunned when he was a kid because of his past, got oh so happy when you showed him a genuine smile. YOU CANNOT LEAVE ME ANYMORE
Yandere roommate who murdered the jogger in cold blood, NO ONE CAN TAKE YOU AWAY FROM ME
Yandere roommate who locked you up forever in your house when you questioned him about his actions, now you're forever his bride, his wife. How lucky for you!!
((This is still an idea btw, so its all subject to change, however the base plot should stay similar ))