everyone of them have their faults. In case of Sid, he could not support Nivedita, when time came and thats his fault. He also could have found ways as u said not to marry Divya, but gave in. So, he has to bear what he did.
Nivedita married Viren forgetting every vow that she took to be with her father and family, and landed up with the same Soods, marrying the younger brother of the man, whom she loved and was taking pheres before.
Viren, used Nivedita against Sid. He is faking and scheming throughout, as he wants to take his own revenge.
Three of them have faults, but there is a reason for all three to have acted such in the given circumstance. Thus it is essential to weigh each with the same scale and not pass a biased judgement.