If you remember couple of his dialogues ...1) post Neha's wedding he tells her that he was so much in love that he didnt even think of spending more time with his sis...there also he didnt think that statement could hurt Sonakshi ...2) Another instance when she asked something like...wont you do it for me ,he said NO..and then he justifies his adamancy by saying that with you I dont need to think what I am talking ...I dont need to put a filter and talk. I could speak my mind out.
So this was expected. CVs have kept Dev's character intact .
What you saw was an absolute emotional breakdown of Dev...He was scared of loosing his mother. His uncles words and his mom's words added to the guilt that "him falling in love caused this issue for his mom. " Him being blindly in love that he couldnt understand his mom.
This is not the first time he is feeling guilty about falling in love as I said above after Neha's Bidhayi also he blamed his love and was guilty. So the next question is ...why is he guilty ??
Because in his life he has never wanted anything for himself. He has lived a selfless life. Here his mom is to be blamed because that lady has raised him in such a way .Anything he gets for himself becomes a selfish act. And we all know that Sona is the only thing till date he wanted for himself.
But above all what affected the most is that his mom did not share his happiness. He doesnt make it verbal but that is going to make him think why ?? This guy is totally messed up...more than Sona he needs a break .
This impulsive decision of his is going to teach him and his family the greatest lesson in life !! Its going to shake the entire Dixit family soon.