You have everything upside down in your head. Helping Ukraine does not destabilize Europe. Letting Putin win does, because destabilizing and dividing Europe is his main goal. He does not stop in Ukraine because winning there will simply confirm his concept of winning wars.
Another wrong aspect is that you imagine that Russia is like UK, a democratic country. It is not, Putin has turned it into a Fascist regime. If you asked what is wrong in Nazi Germany's attack against Poland, then you would be asking the right question - you don't realize why it is wrong because you are not asking the right question.