Can my former roommate sue me for the remainder of the lease or any damage to the apartment? How?

Sure. If you made an agreement, oral or in writing, to co-rent an apartment, you are responsible to the other person for your part of the rent and at least you portion of what damages you caused. Why would you think you are not? The lease is an agreement between the master tenant and the owner of the premises, but you have a separate agreement with the tenant who sub-rented the place or a portion of it to you. and they can go after you for whatever you owe. You had the advantage of living there, why should you not have the obligation of paying?

That would be a yes.