A lightly different version of this happened to me. He was my first BF after my coming out very late, and we began dating just as I was turning 46. He was 52, handsome, kind & very intelligent, and I quickly fell deeply in love with him.
About 4 months after we met I noticed his attitude change dramatically. He became tense & moody, and told me he had to go back on Prozac. It didn't seem to help, and his condition continued to deteriorate. Nothing I tried helped him, and I felt confused & frustrated. I didn't realize men could be so emotionally fragile, my experience being mostly within the Army.
Finally he told me his ex-partner had reappeared, and was demanding half of the private home where my BF now lived alone. I knew there was an ex, but was led to believe that was ancient history. Not so.
My BF started having frequent "meetings" with his ex, ostensibly to negotiate the house rights, and I saw less & less of him. Sensing that I was failing to give him the support he needed, perhaps even adding to his problems rather than helping him, it was I who raised the question of our splitting. He didn't object.
Epilogue: he bought off his ex and kept the house for himself. But another guy quickly moved in with him (I never lived there), who gay friends told me had a bad reputation in the community. Within a year this guy, who had no income of his own, allegedly convinced my ex-BF to quit his very senior position in city government and start his own business at home.
We stopped seeing my ex at his favorite places around town, and friends told me stories about the new BF keeping him under virtual house arrest. I was getting ready to relocate from the area anyway, so I decided to stop by the house and say goodbye, and see the situation for myself. It went like this:
Unknown guy opens the front door a crack: "What do you want?"
Me: "I wanted to see Wayne, I'm a friend of his."
Guy: "He's not home."
Sensing this was a lie, I raised my voice to carry inside the house: "Oh, that's too bad. I wanted to let Wayne know I'll be leaving town soon. We've known each other a couple of years. I'm Tom, and you're...?"
"I'm Wayne's friend, and I gotta get back to something, so..."
"Oh, sure, well is there a better time I can return?"
"No, he doesn't have regular hours." The door started to close.
"Well maybe I'll try phoning, hate to leave without saying goodbye, and..."
"Who's that at the front door?" I recognized Wayne's voice. His BF gave me a guilty look and slinked away as I pushed open the door for myself.
Wayne was happy to see me, and we hugged and spoke inside for a few moments. But I thought I heard feet stirring just out of sight, his BF eavesdropping on us, so I invited Wayne to go outside to see my newest motorcycle.
We spoke at the curb for a while, and I could catch glimpses of the guy peaking out at us through the window curtains the whole time. We promised to keep in touch by phone and email, but that never happened. Emails went unanswered, until the account was closed, and phone calls either went to voicemail, or the BF would say Wayne wasn't home. We've never had contact again, after 11 years.