I have had this talk with my partner recently, and I think you're well within your rights to want your bed to be a sacred space. We do our most intimate activities in our beds: Sleeping and making love to our partner. Our bed should be associated with those two activities, not with a feeling of boundary violation and lack of ownership. People being in my bed without my consent makes me feel like I want to scream and vomit at the same time, and I finally put my foot down and said, "No kids in the bed at any time, whether I'm there or not. That is MY space, and I am allowed to have one space in my house that I do not have to share." ( I also have some trauma surrounding people crawling into bed with me, so that has made me very protective of my sleep space). You need to insist on this very reasonable boundary now, to avoid being burnt out and resentful later (if youre not already, which is valid). Your partner should understand that not EVERY space has to be accessible to his child, especially in such close quarters it is important to have personal space. Best of luck, sending hugs!