Kids won't leave CN and go
Even if the kids r asked n the court they will say CN or say we want both parents together.
If Sai wants to go out, BK will want want both kids n CN.
Above all Sai will never agree to love anyone else for sure, unless BK or P blackmails her for some reason but it won't reach till marriage.
From Sai s side it will be friendship and some gratitude for help.
Acc to me, Sai can be friends and wait till the kids grow bigger and then decide what she wants. She has to focus on kids now.
New relationship puts lot of pressure and expectations from the guy and his relatives, and most guys will want to have kids of his own also. She is also a working mother so most of her time s at work and the remaining time has to be with kids atleast till they grow up.