So far the aid sent to Ukraine (~14 billion) has been less than 2% of the U.S. annual defense budget and less than 0.2% of the total annual budget. While 14 billion sounds like a lot, its basically a rounding error in comparison to the sheers size of the US budget. The U.S. could keep up the current level of investment pretty much indefinitely with negligible fiscal impact.
Ukraine is one of the poorest countries in Europe, the US military aid is literally life saving. Ukraine has a military budget of around 5 billion dollars, they would not be able to defeat Russia without Western aid.
It's just a rounding error for the West, but it is a huge help for Ukraine.
Also and this needs to be said. There is a huge amount of waste in our defense and foreign aid budget (Which I have advocated cutting for years). The support we give to Ukraine has been a massive ROI for US strategic interests to this point.
The Ukrainians have certainly used our aid better than the Afghan government ever did. This war is probably the easiest war since the western front of WW2, to recognize the good and bad guys.
Sure we are sending them a bunch of money but I'd rather give it to them than spend it on a bunch of other things we usually spend money on.
