You don't. It's there for future content that hasn't been implemented yet.
Viewing post in Maids & Masters v0.15.2 comments
For what it's worth, it will open eventually.
There actually isn't a trophy for Lothario's section, though. You can get some extra gear from him if you gain enough reputation during negotiations, and there's an attic and a hidden room with some goodies to find (plus the hidden Elixir that's in every Estate), but that's about it.