Whatever kasturi presumably did with ronak (which was robbies misunderstanding) her family had nothing to do with it. So his behaviour with her family was unwarrented and uncalled for...like someone said whatever kasturi did she did to save her familys reputation. and i dont think she was thinking of anyone (herself or robbie or ronauk) she was only thinking of her family and what they had to go through because or her...i think she behaved in a way many girls would and it is so easy sometimes to catch hold of the first lifeboat when you are sinking without thinking twice. Your first thought is survival...you are not going to check if the lifeboat has cracks and will sink eventually. Your first impulse is to get on it and save yourself and your loved ones. So I dont blame Kasturi for marrying raunak at all.
And now having married Raunak (who for his own reasons married her) she will have to try to make it work. She owes it to Raunak and his family who without a second thought to her 'illustrious' past accepted her with open arms.
She would have been selfish if she had cancelled her wedding with Raunak or (after marrying him) kept going down on memory lane knowing full well that it was a dead end. Yes it is heartbreaking to see robbie go thorugh all that pain but Kasturi is doing what any sensible person would do.
And whatever she feels for raunak is a mixture of fondness and immense gratitude that is manifesting itself the way it is on screen.