If it makes you uncomfortable, then you might have a reason to be concerned. But if you've moved on, it could be their problem, not yours. You can always limit who can view your stories if it really bothers you.
When your ex watches your stories, it could indicate that they haven't fully moved on and still have some lingering feelings. However, it could also be a casual act without any deep meaning. It really depends on the context and your history with the person.
Well, it might not necessarily mean much. Sometimes people just casually look at stories without any deep intentions. They could have just been scrolling through and your story popped up. However, it could also be that they are having second thoughts about the break - up and are using this as a way to keep a connection, no matter how small.