Secret Love

It's not too similar but i kind of get the psycho vibe of both jin and jaemin being like "im the only one that can have him and stuff" but i think from how far i am in secret love its more toned down than secret relationships but they are both amazing BL's in my opinion (edit: it gets past the possessive bit fast but they are both still a bit similar)

Both are about one of the MLs who was adopted having a long time, secret crush on his (non related) brother.