RJ committed suicide at the end of the movie because he didn't want to become a burden in Aarohi's life.
When he overhears her conversation with Saigal (Mahesh Thakur's character) the night before dying, he realizes that Aarohi is going to destroy her life for him.
He knew that even if he could get over his alcohol addiction one day, it would take a long time, and Aarohi would stall her life and career for him until he comes back. His worst fear which was the prediction made by the man sitting in the bar made in the movie, was that she would end up becoming his nurse slash maid. He didn't want Aarohi to end up like him.
He committed suicide to free Aarohi from the relationship. So in the end falling in love with Aarohi just fast-forwarded his fate.
Hopeless romantics would not support what RJ did in the movie. But in reality it's not at all easy to be in a relationship with an addict, and Aarohi didn't want to accept this fact because she was blinded by love.
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