Tarun fighting JAy for Bani sounds little odd.
He was the only person ( may be other than maasi) with whomJay confided in verbally about his feelings for Bani during the divorce drama. Tarun knows how much JAy loves Bani. He is the one who told Jay thatt "Bani Tumhare ander hai " Bani is a part of you that youy can't tear apart from yourself.He was amazed & respected Jay Bani's love for each other.
He can get attracted to Bani because of her resiliece, her stregnth. He can get mad at Jay for his slip. But he sould understand hwat state Jay was in when this mistake happened. He should know in spite of everything Jay & Bnai love each other. He can support & protect Bani but how can he come between them? Won't he do same mistake like Pia. Sorry I know people will be ready to kill me for comparing with Pia. But I just meant that going too much ahead than just being a person to give support & shoulder to cry on.
I don't see how this is possible.