At that point in Donbas Russia didn't invade. They did what the west is doing now for ukraine: providing arms to the separatists and possibly mercenary fighters, after the Ukrainian government sent the army to fight them.
Russia was, by its own admission, either arming Russian citizens in a foreign country to conduct military operations, or it was providing arms to an insurgent group in a foreign country. That's what it admits. The widely understood reality is that it was also sending in troops to those area in addition to the people already in-country.
By contrast, the West is supplying materials to the duly elected government of a country being invaded by its neighbour.
These are not the same things, not even close.
O.