In my opinion Nisha must have realised that Adi also loves her. Remember how he was watching the bracelet?
Anyone remember a day before when Aditya was convincing Jhanvi to drop her home Nisha called someone. I think she must have hired someone & must have threatened Adi that if he wants her alive he must break her heart as well as should support her in getting the same place in the house again. I don't know how convincing it is but the way Adi hates Nisha it is very difficult for Adi to play such a big drama in front of all people. He was looking very happy.So there must be big reason behind it.
And about the mystery man I don't think Nisha knows anything about it so it is impossible for her to take his help.
What do you think guys?
I also think Nisha is not involved in what is happening with Babasa.