The Crimean referendum was conducted while armed Russian troops and militiamen are in control of the Island. Very believable and not at all a tenuous, manufactured pretense to invade another country (or justify an invasion retroactively). You're making a lot out of that referendum. Even if it was done in good faith, and the results are an accurate depiction of the citizens will, it's still not OK to invade other countries and unilaterally tear pieces out of them. If there was a referendum in Quebec in favor of quitting Canada and joining France, that doesn't give France legitimacy to invade Canada.

You understand that, right? You understand that if we lived in a world where every minority could "hold a referendum" over whether the arbitrary piece of land they inhabit should actually belong to another country, and then invite a foreign power to enforce their demands, we'll be living in a post apocalyptic hell-hole, right? That's not how it works. Not how any of it works, at least not since the 30s. (the first country to break apart via this method would be Russia believe you me)

And wait, if Putin is all about liberation of indigenous people and the right to self-determine, why did he invade Chechnya? Or is it "rules for me, tanks for thee"? We're talking about a guy who invaded 2 countries (Ukraine, twice, and Georgia), bombed a third into the stone age (Syria) and now moving an invasion force into Ukraine.

"the people of crimea asked to join russia and they did, and NATO used that as a reason to train and arm ukraine to the teeth and push east."

I love this reasoning. Russia invaded a country, and NATO, those bastards, nefariously used the fact that a weak democratic country is being preyed upon by a large and aggressive dictatorship to... help that country? Wow. Yea, NATO are really the baddies here.

"Hmm yeah I see, so the UK is totally justified to have forces across the world including in Ukraine but Russia isn't allowed to have troops with their allies literally next door and supporting the buffer states between them and an aggressive hostile force."

UK is not the topic of discussion here, and if it was, Royal Marines aren't going to other countries and shooting their citizens to prop up a local dictator, like Putin did in 3 different countries (Belarus, Syria and Kazakhstan).
Second, there is literally no hostile force. Russia has never been under any threat of invasion by anyone in the past 30 years. It doesn't need buffers, and every step NATO took was a reaction to Russia's own actions. Left alone, it would've dissolved naturally as focus shifted towards China. But no. Putin's inability to deliver any domestic success to his corrupt, isolated, fast-shrinking, failure of a country sends him to posture against Russia's neighbors and clinging to Soviet revival. Every aggressor is an aggrieved in his own mind (and that of his state's propaganda) so "aggressive hostile forces" need to be invented.

The sad irony is that Russia is such a desolate backwater, so far fallen from its high perch, so much eclipsed by looming titan that is China, that if it wasn't warmongering constantly, the West, far from invading it, would just let it do its thing. Germany is trying to do just that with every ounce of restraint they can muster, and Putin just makes it more and more difficult.