Right so this is the kind of thing that keeps me up at night reading about at 2am, cheers for that lol.
Three nights in a row is what gets me. One night you could explain away, maybe a pipe or an animal outside or your brain doing weird things when your half asleep. But three nights in a row with a pattern to it? That feels deliberate somehow.
Have you tried leaving your phone on voice record overnight? I'd genuinely want to know if it picked anything up. Also worth checking if the breathing lines up with any specific time, like 3am territory or just random through the night.
The empty house detail is the bit that really stands out to me. No pets, no other people, no obvious explanation sitting there waiting. What does the breathing actually sound like, is it slow and deep or more shallow and quick? That detail matters I reckon. Anyone else had something like this?