Yes, I know this is a show and its all fake but if we think of Pia as a real girl then...
Does Pia really think she would be happy forcing Jai to marry her? She knows that Jai will never warm up to her, proabably not even to her kid.
Its the same deal, when a guy leaves/cheats on his current girlfriend for another girl. Doesn't the 2nd girl realize if the guy /cheated/left someone for her, he could leave her for someone else. I always find this behaviour puzzling, and I guess this applies here too. Is Pia going to threaten everyone the rest of her life?
Can she truly find happiness and peace of mind in such behaviour?