I thibk this is what is going to happen if i understand this character. He is a man of extremes.
Initially it was all about his mom and then came sona. After realizing his love he is making it all about sona but still cares abt his mom but doesnt share or spend time with her like he used to before.
Now from the sbs segments, once ishwari approves their relationship, looks like he is going to take it to the next level. He is going to keep sona all to himself and follow her all around the house (openly this time) and this is going to push ishwari further in to depression.
Looks like ishwari understands her son well and she knows once a girl that he likes comes in to his life, dev will go to other extreme gradually if not suddenly.
I see sona as a sensible and mature girl. She always says NO when ever dev goes over the board- be it gift giving or spending all the time with her ignoring other duties. She still thinks that her parents will be worried if she is late etc. she is doing an amazing job balancing relationships.
Now once dev realizes what he has done to his mom by not spening quality time with her, he will be all guilty and will try to fix the situation by only going to the other extreeme of breaking up with sona.
I believe the story willbe all about how to balance relationships with out hurting ppl we love. Its beautiful and amazing concept and i think it will be a good learning experience for all mil dil and the sons around in the world .