> because he saw that Ukraine ceases to be under Russian influence
This is not true. Ukraine was willing to get nuclear weapons, and use them along with biological weaponry stations all over the border. see «Carribean crysis»
Do you really believe this? NATO refused to consider Ukraine's membership. We were very careful with what we should and shouldn't do in order not to make Putin angry. Now nothing of this matters. We got to the point when Armenia is asking Putin's help and he doesn't have any meaningful force to send anymore.