Why did computer say Nd5 is a bad move?? I did it to force the Q back, then trade the pieces. Tricky spot for opponent. As played, opponent blundered.
Why is this move bad?
While Nd5 threatens the queen and a fork on the king and rook, black can just simply play Qd8 and white misplaces his knight. It's better to trade first (Bxd4->Bxd4->Nxd4->exd4), creating doubled isolated pawns, then you gain the pawn by playing Nb5 which threatens a fork and the pawn. This is a better outcome than the awkward move you made.
Thanks for the replies. I want to get better and this helped.