If Ukraine can stand up (which I'd hope, but don't really believe) and Putin thinks the same way you think he will use nuclear weapons. And he has said clearly that he thinks the current Ukraine is a threat to the survial of Russia. Which is of course nonsense, but that doesn't matter.
The better support Ukraine gets the closer we are moving to a nuclear war. I'm not sure to say don't support them. But don't underestimate the danger of Putin.