I also know I'm not in a position to ask or expect anything of him, but I also feel like if I "let" him be rude to me, aren't I sending the message that his behaviour is acceptable?
I agree with you. Who says you can't expect anything of him? Why is his "bar" so low still?
If you need more in a spouse, you should set the bar where you need it to be, for YOU. And then learn how to lovingly communicate it to your husband. He'll either rise to meet it or he won't, but my advice is often different than the others'. Life is too short, and I'm not big on the whole "Oogh! We mustn't spook him!" thing.
