The Magic Collector by Chesney Infalt

On the day of her wedding to the Crown Prince, Aveline is cursed for helping the wrong person. Not entirely a ghost, she is in between, having no control over what form she takes at any given moment. To break it, Aveline is forced to turn to the man she helped: the ostracised Magic Collector. Sebastian, known to everyone else as The Magic Collector, is shrouded in mystery. His castle disappears, sometimes for months, and then reappears without warning. Curious about him and his collection, Aveline pieces together that he, too, is cursed. As romantic feelings blossom, she is determined to free Sebastian as well—but there are dark costs that expose even darker secrets. Equipped with the horrifying truth, Aveline is left with two choices: abandon the man she loves, or everyone she is trying to return to.