Thanks for reading my post and your comments.
I don't know if M/S are BG "friends". That he is very closed to Dasha, I know, since when Dasha had her own appartment. he saw him there many times. It was suspected that he used the balcony for "romantic" contacts with Dasha. Curiously the last guests are also close to Dasha but I don't know if they are close with M & S.
So who is inviting? Dasha or Masha? Surely that Masha authorizes the invitation, but does she likes to receive them?
By the way, in the threesome, BG performance was far from being perfect. Fortunately Eva "helped" him.
It is a mistery for me why Dasha, after knowing Sasha, is still so interested in BG. Does he has something that Sasha doesn't. Not sexual knowledge for sure!