The vyom flashbacks show two sorts of personalities : a spoilt brat who used to bully n make sharanya bully others and a chasmish character like the one stabbed who kinda seems like a quieter mousy character
Option 1: there are two fully different people, vyom1 is bratty n spoilt, vyom2 is quiet n nerdy maybe, vyom1 is friends with sharanya at college but vyom2 is an invisible type personality who never gets noticed by anyone, vyom2 fell in love with sharanya but only observed her from far, maybe love grew to obsession n led to stalking, at some point vyom2 replaced vyom1 to get close to sharanya and slowly started faking vyom1's bratty personality to be friends with sharanya till eventually vyom2 could not differentiate between his own quiet personality n vyom1's bratty one in his head, the two personalities created identity confusions in him maybe leading to DID dissociative identity disorder/split personality. Now whether vyom1 was murderer or vyom2 don't know...
Option 2: all of the above stuff about two personalities but the only difference is that there weren't two seperate human beings but two identities only right from the start, i.e. vyom already had DID from before
Therefore maybe the mention of City Mental Asylum (maybe vyom's imaginary friend in that hidden dark room has something to do with the Asylum)
Also rajan sometimes seems as if he doesn't care what happens to vyom as long as his final aim is fulfilled, maybe that's coz rajan knows this vyom before him now is vyom2 who has confused his identity in his head n taken on the identity of vyom1 n it's vyom1 who is rajan's son
Option 3: I'm overthinking :P
Ah well it's a mystery thriller n one should be allowed to speculate n do detectivegiri, isn't it.
It's just theory n speculation, hope no one gets offended :)
P.S. on another note, enjoying the flashback scenes.. the SS moments, the trio moments, the shivyom bits, hopefully at some point there will be a continuous stream of the flashbacks over a longer period of time rather than just sporadic scenes, maybe like 2-3 episodes of college flashbacks, that'd be nice, we don't seem to get college campus stories anymore...