Raghu will feel guilty when he finds out

Actually Aman need not tell Raghu, even if Raghu doesn't read the letter he will realise he was the one who kept the parcel at Antu's house when he remembers where he saw Antu's dad. He had even read the board outside "Kaul house". I think he might see the place and remember it when he is in Kashmir or maybe before itself and sadly he will surely move away from Antu at that time. Raghu will never break his promise, so he will always support her but this is a solid reason for him to feel guilty and blame himself for her dad's death. I hope Aman does something about this rather than saying that Raghu kept the parcel, Raghu did it only for Aman unknowingly.

Idiot aman kill him..
Raghu will realise it once Rantara reach Kashmir

raghu is in 4 tons & tons of guilt