Excellent Post
It was a difficult marriage to begin with both were deeply in love with each other yet pulled apart by strains of their family
the marriage ended not because Dev never stood up for Sonakshi no
their marriage ended because of the prenup agreement , if you see that scene where Sonakshi goes to sign Dev wants to stop her but because of his drunk state he is slow .
Dev never had any problem giving money to his wife but she never understood him
she believed Vicky when he said Dev wants them of their house she failed to trust Dev , she failed to believe in the love he held for her
true both had wronged their marriage and it was better that they ended it
now coming to the awards function firstly Sonakshi had no idea that Dev has changed so much so when she decides to thank her ex-husband wanting him to actually know and remember their last conversations to each other but little did she realize the old Dev would have become sad and guilty but not this Dev
yes he blames his mother and Sonakshi for hurting him likewise she too blames Dev for all her pain and broken marriage
both are still very stuck in the bitter painful past and yes both are still very much in love with each other .
about the precap - Dev is not cheating Sonakshi both refer to each other as ex which means they probably had a divorce