My Boyfriend Is Jealous? (Of a non-existent person!)?

I started writing a book about a young couple when I was a teen and in my 20s.

Now, in my 40's I returned to writing the book about the couple - a sort of steamy story with a lot of plot twists and turns.

My boyfriend is supportive of my writing and I've sent him some samples of the book I'm working on, but he said he's jealous of the male character and the relationship in the book???

He wants me to make the characters break up in the book and for the main character to be alone/single. The main character is loosely myself (it's written in first person) and I completely made up the male character in the relationship portion, so it's NOT based on real life or ANYTHING I've really experienced.

Can he be jealous of something or a person that doesn't exist? I'm only being creative in hopes of selling the book as an e-book ect. some day. Also, I've developed the characters YEARS before I met him and I love the dynamics of the story, so I don't want to change it for him.

How can I tell him his advisement is silly and ridiculous since everything is made up and he has nothing to be jealous of???