I think they can both be blamed but their characters actions make sense.
Aditya has nothing left to lose he sees his whole future with Zoya if he can't be with her then what's the point of living. He's been through a broken heart before and can't do it again, so he has to put all his efforts into making Zoya realise. He doesn't care about anything else hence his impulsive behaviour. He said that he would never let Zoya cry again but he's not realised she's only crying for him, because he's trying to save her from being in a loveless marriage and doesn't care about himself or anyone but only Zoya. He's never been in love like this before and can't let it go at any cost because if he can't stop the wedding there's nothing left for him, Zoya is his reason for living.
Zoya has a real battle between choosing between her Dad and the person she loves, a position she's been in before where she made the wrong decision. Aditya had helped build Zoya's confidence again but her dad with his constant taunting has taken that away from her. Aditya showed her it was okay to trust and believe in herself he was her support, she fought for him in front of everyone because she trusted him so much. Her dad also took away that support from her by proving that Aditya can't be trusted either. She is almost back to the same state she was in after she found out about Yash's betrayal, no trust in herself and this time Aditya isn't there as the friend she needs to bring her back. She'd rather follow what her dad says even though it is so painful for her because she can't be blamed again, she has no confidence in herself to make the right decisions. She wants to do one thing but is doing the other to please her father, she can't have him hate her again and speak bad about her the way he was when she overheard him on the phone at the very start.
She mentioned at the start something along the lines of that love is trusting the person you're in a marriage with. She had that with Aditya she trusted him more than herself. However now because her father proved Aditya wrong she's back to the point where she can't even trust herself, her father showed her that she can't pick the right friend either. Even though she doesn't want to she probably feels like it's better to listen to her dad than to be hurt again like she was with Yash.
The episodes do seem to be dragging a bit, but I guess they have Adiya scenes in them and allow us to see how the characters more. It's also a wedding track and itv always seem to drag these for a long time as there's always drama.