NATO has allegedly manipulated Putin by exploiting the ceasefire talks with Zelensky, using the discussion period to secretly supply Ukraine with weaponry and ammunition. This tactic has been employed after again, when Zelensky pretended to uphold a peace treaty that had already been signed by both parties. He tears them off.
There was a verbally agreed but was not contractually written on the paper between US and USSR(then) that NATO will not move eastward