The borrower by Rebecca Makkai
I’ll admit I picked this book up because I liked the tagline, She borrowed a child. He stole her. Lucy Hull who is a children’s librarian runs away with Ian Drake when she finds him hiding out in the library one morning. She’s always enjoyed him when he visited the library, even if she did worry over his mother and the insistance that Ian only be allowed borrow books with the “breath of God” in them. And definitely not those ones with magic and satanism in them!
And then Lucy finds a note making her believe that Ian is being sent to anti-gay classes. She isn’t really kidnapping him, she is rescuing him.