The Elephant in the Room:
I am very sympathetic to you - not because I have a writer spouse, but because given the chance, I'd be obsessing about my latest work and talking about it constantly. Is your husband Asperger-ish? If so, this is a common issue.
I think your spouse likely cares for you and appreciates your support. BUT an obsession is something that grows to fit the size of the room it's in. Rather than allowing it to dominate everything, you probably need to set some serious guidelines about then writing can and can't be discussed. I'd select a specific hour(s?) during which you talk about his work. Outside that time, it's verboten. But give him at least SOME time for the writing. It is his passion, and he wants to share it with you.
Writing as work has no set hours. So it's up to the two of you to make rules. It's HIS work, and you can support him by letting him have time to work on it, but then designate time when work is forbidden - date time, if you like, or relationship time. Dinner is a good time, unless he loves talking about his book while eating (if so, then the rule should be he can talk but you're not required to respond). Regardless, there needs to be set time when the book is off the table. Before bed is another good time, and can help with sleep.
It's okay for you to NOT love his work. If you don't care for it, be upfront that your feelings for him are not your feelings for the book. If he can't accept that you may not be passionate about it, then he's got more serious issues. Use the beta reader justification if you need to - if you let yourself get too involved with the book as a reflection of him, you can't give useful criticism when something comes off flat. So maintain as much space as you need for your sanity, and justify it as impartiality. Unless you're prepared to go all the way down the rabbit hole with him, keep yourself as you. He loves you more than the books, and will accept it from a place of love.
- PS I think this will get closed, but if the site isn't for helping writers, then I'm not sure what the point is.