Will the west at some point grow tired of sinking money into the Ukrainian war while poisoning their own economies with sanctions, making domestic porkies sad?

I think we're seeing the beginning of that with the UK waiving the sanctions on Gazprombank so they can access natural gas, and the EU capitulating to Russia's program even if they make it appear to be a victory over them in the media. And with Greece and now Germany effectively running out of weapons to send to Ukraine. I'm trying to stay out of the prediction game here, but I think it'll take at least another month or two before the west starts to serious undo the sanctions on Russia, but that will either have to be because they convince their fellow countries and their people that the particular sanctions they want to undo are causing more harm to themselves than to Russia, or it'll have to be Russia ending the invasion after they claim the Donbass. And that's at least a month out, unless Ukraine makes a serious retreat in the coming weeks.

Will material conditions eventually break down liberal idealism?

Yes (or they'll starve, whichever comes first), but it's unclear to me how long it'll be until that happens. We're dealing with the most propagandized people on the planet, who have been subjected to a century's worth of research into how to manipulate people both as individuals and in crowds. It's not hopeless, far from it, because the general public still have their material interests aligned with communism and they understand that when they're broken free of their liberal stupor, but it is a challenge nonetheless.