The same way Abhi justifies all his poor behavior - he's doing it to protect his people. Pragya is now Purab's di. He cares about her by virtue of Bulbul caring for her. If he's going to make a sacrifice, it better be worth it in protecting Pragya and the Aroras. And who cares if Abhi doesn't like the arrangement? Purab doesn't like the idea of being married to Aliya; Abhi certainly doesn't care if that was the case. He prodded them along to this point anyway. Why should Purab consider Abhi's feelings when Abhi never bothered to consider his? (Didn't even bother to check with him about how he felt about his mystery girl before he married the alleged girl)
I don't know if it will happen but it does help prolong the MU.
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