Nattu was working under Pia in WGI.
He was there under masquerade to evaluate JW's strength. At the same time Pia was hitting hard on JW and he shrugged her off everytime. Nattu due to close proximity to Pia noticed it and thus planned where to hit Jai, so that he is badlky wounded emotionally. Pia was desperate to get JW and he was not willing to give in to her fake charm. Dubai deal brought an opprtunity for Nattu to play his game. He contacted Barnali and she inturn contacted Pia and posed as her well wisher and gave her the idea and supplied her with the drug to intoxicate JW. She planned everything that happened that nite and Nattu is the man behind CD. bani reten gave him more ammunition to hit JW with. Here is what I based my assumption on:
Tony still at WM. Pia receiving calls from Tony . Interaction between Nattu,Barnali and Pia not shown till date after he revealed his identity even in Dubai. Nattu has been to Jail only once to meet his mom when Tarun was there, maybe he faked all that yelling at Barnali to get through Tarun and finally to WM. Barnali has a track coming up post leap.
Tarun post leap will just be over protective and in love with Bani and thus will not allow JW to come near her out of jealousy. Reason for JW to come back will be the threat and danger he will forsee to Bani's and his childs life from Nachiket as he still will be hovering around WM as they will the legal owners of WGI and WM. His journey post leap will start with suspision of him being framed by someone and that someone may turn out to be Nachiket. And the rest of the clan will just face his fire in the process.
It is just an assumption and made some sense to me.Tell me what you think