When publishing, should every author officially sign off on the final work?
It's rude and obnoxious, but it's not illegal and depends on your relationship with the offender whether you want to try to do anything about it. I have a paper that I never saw before submission and whose conclusion I would have qualified in a different way than what was submitted and accepted for publication. I keep my eye on that group of people now so that it doesn't happen again. I never complained because I wanted to keep the relationship on decent terms. 

It's not ethical, but calling the publisher and asking for a retraction is probably your only defense now that the article is published. That's not really great for you, and it will probably destroy any relationship you have with this person. Saying something about future papers can probably be done tactfully, but I'd still be careful. 

What I don't see is how this demotivates you. Papers are being published with your contributions in them which will still contribute your value to future employers. If you had an expectation of author order, that should have happened before the writing was started, and really before the research was begun. That's a conversation that can still be had before other research continues.