tricky!
the first christmas after husband left, i ended up spending more on him than anybody else (with the exception of son) and got the most gawdawful beaded necklace thingy (i can't believe he even picked it out...) and a candle. this from the man who used to buy big rubbermaid bins to use as my stocking. i was heartbroken, not from the lack of gifts but because of what it represented. i still hadn't found out about OW at that time.
i would not buy husband a gift if it weren't for son, but what i now get him (same every year - doesn't even have to bother opening it, because i'm sure he can easily guess) is a 5x7 of son's school pic (i bought him a frame for the second christmas after he left - he can change that out or not) and a $25 gift card for son's favourite restaurant so they can go together. last year, during his failed return attempt, i added a couple of cigars and i'm glad i didn't go overboard because within a month, he was gone again.