Now, there was a verbal agreement that NATO wouldn’t expand into the east,
There was an agreement that no non-German NATO troops would be east of Soviet/Russian troops in Germany. And they weren’t. Russians took their good time to withdraw after reunification but they were allowed, as is proper, to do it without Americans between them and the eastern border.
(requiring no NATO troops at all would’ve been unrealistic as the NVA (East German army) got swallowed whole-sale by the Bundeswehr).