For Worse by L. K. Bowen

Wait Until Dark meets Gone Girl in For Worse, a debut thriller that pulls the reader deep into a dark web of sinister plots for marital revenge.
Ellie is leaving her husband ... again.
After twenty-two years of marriage and an unsuccessful separation, she can't take it anymore. On the surface, she has a picture-perfect relationship. Jeff has been a steadfast spouse. But what seems like loyalty is in reality an obsessive desire for control. Ellie is slowly losing her sight, which means she needs more and more assistance, and Jeff will stop at nothing to ensure she feels helpless and reliant on him alone.
Determined to escape her psychologically abusive marriage, Ellie turns to an online chat room full of like-minded women in the throes of divorce. Despite their anonymity, these women quickly become Ellie's closest confidantes. The chat room is a refuge, a place to which Ellie can retreat for solace and support.
Jeff continues to be manipulative and cruel, using Ellie's failing vision to gaslight her into questioning reality itself. Desperate for freedom, she sinks deeper into the online world and is drawn into the dark web, where she discovers a group of women with a shocking solution for ending a marriage.