Considering Fredersdorf's marriage plans are official in December 1752 (when Lehndorff spots his fiancee at a social gathering and also already knows Fritz is going to give her 5000 Taler as a wedding present), though the marriage itself doesn't take place until one year later, while Glasow doesn't show up in Lehndorff's diaries until the 1755 Fritz trip to the Netherlands, I'm thinking you're right. Also about the projecting.

BTW, going back to both German and English wiki for Fredersdorf to check for the marriage date, I have to go wtf again at the utter lack of source citation for the "dismissed for embezzling/died broken hearted about his lost honor", but the entries at least mention that Fredersdorf's bedroom in Sanssouci was directly next to Fritz', is intact and can be visited today. So you must have seen it when you were there, unconsciously?