May be in that sona might come to know that ishwari will never be happy for dev and sonakshi and in todays segment even erica said that sona knows that ishwari will never be happy
If we see sona doesnt know this because even in hospital scene during breakup she wanted to convince his mom about his relation next day she might got the hint about this but after confrontation she might realise that she can never be happy !!!
That''s why sona may ask dev to forget her not to follow her and no trying business !!!!
This promise not only kills them but even kills us !!
Donnt know how long they will keep this promise alivee