Honestly, maybe you should just respect people’s privacy. If someone has decided to unfollow you, they probably have their reasons, and trying to secretly monitor who unfollows you seems a bit obsessive and, frankly, a violation of trust. Instagram doesn’t notify users about who checks their followers, precisely to avoid these kinds of privacy invasions.
If you truly care about your followers, focus on genuine interactions and let go of the need to track every change. If they wanted you to know, Instagram would make it public!