First of all ... I always recommend having a good relationship with your neighbors so that you at least have some idea of the "intentions" of your neighbors. Just a good idea in any community.
That said, the legality of a neighbor stopping the new owner from using the driveway depends on how it is shared and potentially how your State would interpret these situations.
Is the driveway truly deeded as a 1/2 and 1/2 split? Does one of you own it and the other have an easement? Does one of you own and been simply allowing the other use?
Ultimately, it boils down to how it is deeded. If you own the property or have a deeded easement on the property, then your neighbor can NOT deny the next deeded owner the same access. All the other arrangements may depend on how your laws treat such arrangements and you'd probably need a lawyer to clarify it for you.