There are a few possible explanations here, and not all of them are about you or the relationship.
The most common institutional reason is a facility lockdown. When a lockdown is called, all visits are suspended across the board, sometimes for days at a time. The inmate does not cancel individually in that situation, the facility cancels everything, and communication during a lockdown is often restricted as well, which is why you may not be hearing an explanation from him directly.
The other possibility is that he has lost visitation privileges. Incident reports, disciplinary sanctions, or certain classification changes can result in visits being suspended temporarily. If that happened, he may be embarrassed to tell you or simply unable to reach you to explain before the visit was canceled.
It is also worth considering whether there is something going on with him personally that he has not shared yet. Sometimes inmates pull back from visits when they are dealing with something inside, a conflict, a mental health struggle, or news about their case, and they are not ready to talk about it face to face.
The most direct path to an answer is to call the facility and ask about his visitation status. Start with the unit counselor. They can tell you whether visits are suspended facility-wide or whether something specific to him is affecting his privileges. That conversation will give you more information than waiting and wondering.