So you believe the invasion to be justified?
I think the situation is too complex for me to say whether it was justified or not. What I will say is that most if not all geopolitical conflicts can be solved diplomatically.
Russia gave their terms which were expressly rejected by NATO with no concessions whatsoever. NATO continued to push aggressively into Europe up to the Russian border. As a military alliance, that could be a considered a threat to their national security. They have also had geostrategic plans to develop gas reserves that were discovered in Ukrainian territorial waters and use that to supply natural gas to Europe, cutting off Russian gas supply - hence the annexation of Crimea. So there's both an economic and national security element to it. There's also the cultural element which is the Westernization of Eastern Europe, thereby reducing Russia's sphere of influence in the region.
At the end of the day, it's the ordinary citizens that suffer.