Responses
https://www.mangago.zone/read-manga/romantic_lament/ is really the only one i can think of and it's not even close to this but it has similar themes of neglect by the original partner.
https://www.mangago.zone/read-manga/love_or_hate_yeongha/ kinda fits i feel
Any bl recs where the bottom is together with his boyfriend, but the boyfriend doesn't really pay attention to him but always did with someone else so the boyfriend's best friend just came and spend time with the bottom instead.
Doesn't have to be exact like this, but y'know (づ￣ ³￣)づ