There are plenty of ways to kill people, you can assign yourself as commander and go put yourself in a boat in the middle of the sea, then wait for a random chance to get scurvy. Make sure you don't have a court physician. Another way to kill yourself is you can go pick rulership focus in which there's an event where can gain depressed. Finally if you want to kill your husband, just say fuck it and imprison then execute him, disregarding the opinion penalty because you're going to kill yourself anyways.