Yeah definitely need Devs side of story for audience to connect. They need to reveal back story for Mannats hatred for Dev. As you mentioned she failed to notice his transition once Jeet told Dev he loved Mannat. So this crazy hatred is uncalled for. And of course Mannat knows that the reason Jeet was out the day he died was he wanted to give her the ring. So her still blaming Dev for Jeet’s death doesn’t have a strong backing.
Yes I can understand her grief of losing her love, but this hatred for Dev doesn’t have a strong background. And Dev pov has to be explored more.