My new supervisor wanted to collaborate with my ex-supervisor who bullied and destroyed me
What will happen depends a lot (too much) on the good will of your new supervisor. But you have to avoid getting trapped again even if you aren't in a good will situation. 

You will need to insist to your new supervisor that you cannot work with the old one based on past interactions that you found destructive. Also inform the supervisor that you find the actions and attitudes of the other student to be very unhelpful and that pressuring you isn't going to resolve anything. 

Sadly, I can't predict that the outcome will be positive, since I don't know anyone involved here. But, you might also have to consider that you need to find a new situation altogether if the new supervisor turns out to be unsupportive. 

But don't make a point of discussing your view of the competence of the other student. That is for others to judge and raising it won't help your case. 

You need positive supervisor support and you need to not have to deal with social pressure. The pressure of research should be plenty.