I really don't tell anyone anything about my therapy. It's private. You should only share as much as you are comfortable with, and don't be afraid to tell nosy people that "it's private," or "that's confidential," or something generic, like, "I think therapy is helpful to me." For dealing with your fiance, you could not mention your T visit and maybe he won't either--he'll respect your privacy. If he does ask you something, like "how did T go?" you could just say "fine," and leave it at that. When you don't elaborate, hopefully he will get the message and you can move on to other topics of conversation. If he pries, use the "it's private," response.

Good luck!