Leaflet: how to display a unique marker per map
I would use a contextual filter (Advanced settings column) based on the content NID (node identifier). You will get a settings window where you choose "Provide default value" and Type : Content ID from URL (the nid is always available from URL even if you use an alias). Then, the Leaflet map will be filtered using this NID and you will get only one marker (display all results and remove your sort date) created with coordinates entered for this specific content (page). Finally, you will need only one block with this contextual filter, since it will be automatically modified according to page URL.

Hope this helps.