Yes he did lose anything, before he saves his Di's life and before he marries Khushi ... his childhood was a misery for him, imagine how bad it must've been that he started to hate GOD, started to hate the word "LOVE" ... He was thrown out by his paternal family, he had to suffer at a young age, and imagine at such a young age he's a business tycoon, therefore that concludes that he had to work sooo hard in his childhood, that he had no memories of what its like to be a kid, to be innocent ... and then when finally his heart starts to melt, His Arnav side comes up ... he sees the worst night-mare in real life, the woman he loves with another MAN let alone his own Jija jee ... only we as viewers know that Khushi is innocent, but Arnav doesn't ... to him what he saw he believed, now he's no god he can read Khushi's mind can he? so what do you expect ?
to save his sister's life did he lose anyting?.big NO..but we know that kkg lost everything she valued in life...members are talking about that he will send her back to her house after 6months..and do you think they will take her back and treat her well?..and why men have to decide women's fate.