My T always takes two weeks off over Christmas, but I've never struggled with it more than when it's in the Summer of Spring.
I'd tell my T about struggling with it if I were you. Lots of people find Christmas a difficult time and if he already asked, I'm sure he's prepared to hear something about it not being a great time. If he knows that you're having difficulties with him taking time off, he might be able to brainstorm some things to help during that time. I doubt he'd feel guilty for taking care of himself afterwards.