Can someone tell me how Love Nest is a spin off of this??? I got lost in transaction.

http://www.mangago.zone/read-manga/change_world/
This is continuation of Sayonara game. And there are answers to your questions (⌒▽⌒)

The main character in love nest (masato) is the friend of the main character (arimura) of this manga and it's sequel, he shows up many times in this story and the sequel, he actually flirts numerous times with the guy arimura likes and gets into a relationship with. Love nest is essentially a separate story about masato, his past and his love life.