They are standing up for themselves and fighting their own battle, we're just helping even the odds by helping with better equipment.
Actually, very few of our tax dollars -- as a whole -- are going to Ukraine. Instead, we are largely providing our old equipment to Ukraine, with replacements that were already scheduled that are newer and have better capabilities. Now, yes, we are aiding them with ammunition that we are having to replace (though, honestly, even some of that is older and needed to be replace due to being at its expiration date), though in those cases it is still ammunition built in the US. The fact is, 90% of the money "spent on Ukraine" is actually being spent in the US, for US goods. Even more interestingly, some of the equipment being provided by our European allies, such as the F-16s, are "aiding" the US -- as their replacements, the next generation fighter, is being sold to those allies after being built in the US.