He could be busy. His schedule might have become packed all of a sudden, leaving him no time to check Instagram stories, not just yours but perhaps any at all. For example, he might have started a new job with long hours or have a lot of personal projects to handle.
You could start by posting more interesting and engaging content. For instance, if you usually post pictures of your daily routine, try adding some unique and exciting elements, like behind - the - scenes of a hobby or a special event. This might catch his attention again.
It could also be that something in the story made him uncomfortable. For example, if the story contained topics that he didn't like or disagreed with, he would choose to stop watching it. Also, perhaps he accidentally clicked away and then just forgot to come back to it. There are many possible reasons for this situation.
There could be several reasons. Maybe they're trying to move on completely and avoid any form of connection, even the passive one of viewing stories. Or they might have found new interests on other platforms and are no longer as engaged with Instagram. Another possibility is that they're respecting your privacy more, especially if they think their viewing might make you uncomfortable.
If you still care about their opinion, you might consider reaching out privately in a very casual way. Just ask how they're doing and mention that you noticed they stopped watching your stories. But be prepared for any kind of response, positive or negative. However, this is a bit risky as it could reopen old wounds or create new drama.
It's possible that he lost interest in the content of your stories. If your stories have been about the same thing over and over, he might have gotten bored. Another reason could be that he has found other sources of entertainment or information that he prefers.
Perhaps there was something in one of your stories that made him/her uncomfortable. It could be a topic, an opinion or even just the way you presented it. So he/she decided to stop watching.