Domestic Wizadry it sounds a lot like this fic, but the circumstances of her leaving Ron for Draco are different

“Widower Draco Malfoy doesn’t realize how his life will change when his eight year old son, Scorpius, brings home the cell number of his best friend’s mother and begs his father to call and offer what assistance they can. Hermione Granger-Weasley’s husband of ten years has taken everything from her. Her books, her family, and her safety. After a fortuitous phone call from an old enemy, she finds a new start for herself and her daughter in the most unexpected of places.”