Demand My Time to Work

I am only on my third week as a scholar. Thank you for your time in reading my question.

I quit my job three years ago and my husband and I decided that I will not look for another job but instead dedicate my time and write novels.
During the first two years I spent time going to seminars, conferences, workshops and read tons of books and got very little writing done. Mostly, now I realize, I feared writing.

My husband supports us both financially and now that I’ve decided to get to do the real work and scheduled it on my calendar, every few weeks something comes up and I am unable to do my work.

My husband asks me to take care of his sick mother when he is away, he asks me to make time in the middle of the day to meet friends who are visiting, and each time I do that I feel resentful because I have a thought that “since he is supporting us both, I should ‘do my part’ by complying to marriage obligations I might not like doing but which I should at least do those.”
I know that if I did have a regular job he would never ask me to tell my boss that I can’t show up this week because I need to take care of my mother in law or I need time off in the middle of the day because I have friends who are visiting from out of town.

If I understand from your teaching correctly, he is allowed and probably continue to make requests.
I am allowed to decline those and tell him I have work to do.
He is allowed to feel bad about it. And he might even say, ‘then go get a job.’

When I do thought work I get two conflicting feelings: On one hand, even though writing is the scariest thing for me now, I know I do wish to give it my all, overcome the fear and get a complete novel written.
I also don’t want to get back to looking for a job. I love the idea of being an author and making it on my own.
So it’s true, one might say I wasted three years, but I know these years served a purpose for me. I am only ready now. I could never be ready before.
How do I demand my time to work from a positive place?