Your post is lovely and I want it to be true, nevertheless there are few points which make me differ a bit.
1. I think when Arnav said "I love you", he really meant it. He knows it is the truth and he has been aware of truth for quite sometime, much before Khushi became aware of his feelings.
2. His life is in danger and right now the situation is exactly like the last scene of Heer Ranjha. At this moment he has heard Khushi's side of truth which is contracting what he saw or thought he saw (the terrace scene) but right now for him
"pyar mein kuch sahi nahi, kuch galat nahin " but the emotions of his love for Khushi are far intense than the rationale of mind and battle of logic. She may be innocent, may be partially innocent , may be not, IT DOES NOT MATTER. "Sirf yeh sach hain, ki maine tumase hamesha se..." . Now when he is thinking that it is last chance , he is completing the sentence.
3. That is the reason he is worried for Khushi, and asked Akash to take care of her. The thought of whether she loves Shyam or not is irrelevant here. That is how true love is like he could fight his own demons and could see the truth of love.
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