I think countries should always defend their allied regardless of the outcome, since they are ALLIES

I think it depends on the situation entirely. If it's a bad ally like Israel, then no the US should not defend them. Also if a country's economy is suffering and it is heavily in debt I think that's a consideration. The US has already gone far and beyond what we were morally obligated to do with Ukraine. On TV there were ads with celebrities begging people to donate to the victims of the Maui fires. That is completely backwards of the way it should be. The Maui victims are US citizens who pay taxes, they should get government aid first. Then let people donate their own money to Ukraine or Israel if they want to help those countries.