Well to play the devil's advocate, he doesn't know under what circumstances Rusty agreed to marry Samay... so this punishment is actually for both of them.... though i think its easier for him to think of it only as making Samay unhappy.... by thinking of it as revenge against Samay, he can rationalise what he's doing to his daughter....also he has not bought the "they're good people and my kids" theory.... he still thinks that they are against him and so he's trying to break them up.
Must say Mathura and Biji are most inconsistent....
Randhir at least is pretending.... they seem to have forgiven and forgotten everything.... just two weeks ago they were screaming at Rusty so badly, in that episode when Samay asks her for divorce.....i think the change in their attitude comes from the rush to end the serial, par yeh change, especially in Mathura, mujhe bahut weird lagta hai.