So I may have figured out what happened with the "confidentiality" breach.
We talked about it again, I insisted on the name of who said something but he refused to give me any name declaring that it hypothetically wouldn't be fair to the person who may or may not have confided in him. He also said that the reality was that he'd just "heard stuff" that hinted at people knowing more than they let on, which is entirely plausible. I'm still not sure which of these versions is true but I'm guessing the latter if any at all....
What I do think happened though is this:
the day before he got weird I had a student of mine here, she's actually a good friend and we've been through a lot together and talk about most anything including our relationships. She's not the closest friend I have, but she is one of the people I talk fairly openly with because she's not super tied to my group of friends.
She asked how things were going between us, as well as with my health and I spoke fairly openly with her, she even asked how our sex life was (to be honest we haven't had sex in a fair while). Bf was "studying" in another room with the door closed, we were talking quietly but there's a good chance he overheard part of our conversation. I didn't care at the time, I knew he might hear, but I wasn't ultra careful, I didn't think it would bother him really, I was just being open and honest with her. Then I forgot about the whole episode.
I think what he then did was, he used that conversation as a staple for people who are close to me. I think he just guessed on Mr.XXX. He knows we meet rather often for lunch so it was a fairly easy guess to make. I may still ask Mr.XXX if he knows anything (when I see him... who knows when) but I'm certainly not angry and I doubt he'll admit to anything at all even if there had been a breach.
What I do know though is that human nature gives in to gossip, behind people's backs often. It's just the way the world works. Not everyone engages in this but most do and I myself have contributed to the nasty business. I generally know when not to open my mouth because of really sensitive material but on more minor subjects I have discussed it with others despite knowing it was somewhat of a "secret". Problem is that often people figure secrets out before they are said so there is a lot of conjecture going on before it's actually let out of the bag. I even remember people getting really radical horrible ideas about what others have been up to and having to let a minor "secret" out to appease the much more horrible conjecture gossip forming before my eyes.