Our cat Millie has previous with this too. Given to me as a young cat, she first went missing at about a year old. I found her a couple of weeks later after neighbours had seen her going in and out of an empty cottage at the edge of the town. When I turned up she let me pick her up and take her home and she happliy stayed home for the next year or so (I still have no idea why she moved out).
The next time she went missing I gave up hope of getting her back. She was away for about 3 months, I had just decided to throw her bed and toys away when the local cats protection guys got in touch. Apparently someone in the adjoining town took her to the vets to get her ‘jabs’ as they thought she was a stray and intended to keep her. The vet thankfully read her chip and I got a call, it was lovely to see her again.
That was 5 years ago, and she has stayed with me since. Even though we have brought home new dogs (and kids), she hasn’t decided to go walk about again (yet). I never worked out why she went, it was just always good to see her back.
I hope your fella comes home soon!