Can someone share your close friends story?
Mostly no. Since close friends stories are made to be a private sharing experience among a specific set of people you select. It's like an inner circle thing, and sharing it outside that circle without permission goes against the purpose. For instance, on Snapchat, the concept is similar. The close friends' content is not meant to be spread further without your say - so, no one should be sharing your close friends story without your okay.
No. The idea behind close friends stories is to limit the viewership to a particular group. It's a form of privacy control. Reposting or sharing it without permission violates the privacy boundaries set by this feature. Platforms are usually careful about protecting the privacy of users' content in this regard, and they would not allow others to share or repost your close friends story without proper authorization from you.