Something drifted, and nobody has named it

What this means

You are not describing secrecy. You are describing distance. One or two things are different from how they used to be, and each of them, taken alone, has a perfectly ordinary explanation: a new job, bad sleep, a rough stretch with their family. Replies come slower. An evening looks like two people in the same room doing separate things. Closeness got quieter without anyone deciding it should. What is actually bothering you is not any single item on that list. It is that the room feels different and nobody has said so out loud.

This is not a diagnosis and it is not a verdict on your partner. Nothing you reported establishes what they are doing. What it does establish is that something in the relationship changed, that you noticed it, and that the noticing has had nowhere to go for weeks.

Why this happens

Drift is the most common thing that happens to long relationships, and almost nobody chooses it. Two people get absorbed by work, or a baby, or a parent getting sick, and the small maintenance rituals quietly fall off the schedule. Six months later the connection feels thinner and neither person can name the week it started, because there was no week. It simply eroded.

The reason drift gets mistaken for something worse is that the felt experience is identical. Your body registers the withdrawal of attention long before your mind has an explanation for it, and then supplies the most vivid one available. It is worth saying plainly that ordinary drift is far more common than an affair, purely because there is so much more of it in the world.

It is also true that distance is one of the conditions under which affairs start, not because drift causes anyone to cheat but because unspoken distance is where a lot of things grow. That is not a reason to be afraid. It is a reason not to leave it unnamed for another six months.

What to do next

Ask about the change, not the cause. Opening with "are you cheating" turns the conversation into a trial that both of you will lose. Opening with the observation gives you somewhere to go: "The last couple of months have felt different to me, and I honestly cannot tell if it is you, me, or just this season. Can we talk about it?"

Pick one concrete thing rather than the whole atmosphere. Atmosphere is impossible to answer. A specific is not. "We used to eat dinner together on weeknights and we have not in about two months" is a sentence someone can actually respond to.

Then watch what happens over the next three weeks. Drift responds to attention. If you name it, ask for one thing, and things ease, you had drift. If naming it produces defensiveness, or the changes keep stacking up rather than settling, that is genuinely different information and worth taking seriously.

If it turns out the distance is not a season but the shape the whole last year has taken, a wider look at what the relationship is actually doing will get you further than more questions about fidelity.

What this is not

This is not a reason to start monitoring anyone. Surveillance answers a question you do not currently have and costs you something you may want back. Right now the useful move is a conversation you have been putting off, not a search.