...

It's pretty obvious he's been faking from the start-

Nope, on chapter 101 after everyone leaves the hospital room, he panics and looks at his phone thinking to himself "Why has everything, including my building, been transfered to Dojun Jeong??"

At least at that moment in time he has no memory of dojun. Jaehee also thinks to himself a lot of things in that chapter like "who is that guy? his name is dojun, right? omg is that one guy I had a crush on..." etc.

Also, when he confront's dojun's cousin by saying the uncle ran over someone with his car in a hit and run, the cousin asks "How do you even know that?" and he again, thinks to himself, that he has no idea how he found out about it, it was written on his phone.

So yeah, it is not "pretty obvious" because he was NOT faking it from the start
(〜￣△￣)〜

Ok at the start it wasn't obvious I definitely worded it wrong, sorry (￣∇￣")its just I remember at some point his memories come back in full but he doesn't tell dojin about it cuz he takes advantage of the fact that he got amnesia to continue scheming whatever he was scheming to protect dojin

Σ( ￣□￣||) AAa I see, thanks!

The pacing got me a bit confused >_<"