War on Ukraine, is it the US job to help?

I hear a lot of debate in my area around this. Especially with my partner. And I won’t lie I have not been too familiar with what’s going on there. But from what I understand, Russia wants to stop them from entering NATO, and take over certain areas of Ukraine? Is that correct? If not please share, I want to understand more. My thoughts are, since the beginning of alliances, other countries have helped fight wars for those in need. If a smaller country is being invaded and dictated, is it not the duty of those alliances to help and ensure freedom and peace within those countries? Or do we not involve ourself in others wars and let another country invade without any interference, to protect our own troops? My partner believes we should not ever involve ourselves for other countries & risk our own troops for what he is calling “a pointless war”. Like I said I’m not too familiar with what’s going on, but I find that extremely morally conflicting. But I guess I need more of an understanding.