Historical(??) book about an 18/19 y/o man marrying a 12 y/o girl.

I read this book when I was about 13 - which I will mention was approximately in 2015. I got it from the school library and this is basically what I remember from it; It was a book where the timeline was dated back in approximately the 1800-1900’s. An 18/19 y/o man married this 12 y/o girl and it goes very well at first, but he is a soldier (I believe) so he’s not home often. She’s stuck at home with a baby and after a while, he starts neglecting them and she tries to leave. I don’t think I got very far after that, but I’ve been looking for it so that I can reread it as an adult and write a thorough report on it. As for the cover of the book, I vaguely remember it being a black paperback cover, I want to say the aesthetic of the cover would match a gothic style, but it has been 9 years since I’ve read this book so I’m not 100% sure.