He cancels plans and goes offline for hours: what to say

Read the cancellation itself first. Was it a few hours' notice or the same afternoon? Did he give a reason that sounds real, or a vague 'something came up' with no follow-up? A late cancel with a specific, plausible reason and a suggestion to reschedule is different from a late cancel with nothing attached. The first is a busy person being imperfect. The second is someone who has stopped putting effort into the plan.

Then look at the silence. Hours offline after a cancellation is common, especially if he is at work or dealing with whatever came up. The question is whether he has been reachable on other days. If he normally replies within a day and this is the first gap, that is information you can work with. If the pattern is that plans fall through and then he goes quiet for a day or two every time, you are looking at how he treats you when something more convenient appears.

Your reply has to show you received the cancellation and that you are fine with the plan changing. It should not reopen the argument about whether he was rude, and it should not offer him a way to make it up to you by being very apologetic. Acknowledge the change in one short line, then decide whether you want to reschedule. If you do, put a day on it. If you don't, say so plainly.

You also need to keep your standards in the reply. If he cancelled late and you are not going to act like it was nothing, you can say that in a sentence that is not a complaint. The aim is to leave him knowing where you stand without giving him the emotional weight of an accusation to respond to. People who are interested usually respond well to a clear, unhurried reply. People who were only half in tend to get vague or disappear further, which is useful to know.

If you are going to reply, do it at a time when you are not running on adrenaline. A message sent at 1am after six hours of watching the screen reads as anxious even when it is not. Waiting until the next day usually produces a better message and gives him room to come back on his own terms.

If you have sent one reasonable reply and he has not responded within a day or two, do not send a third. Two attempts at contact after a cancellation is enough. If he does not come back with a new time, the plan is effectively dead, and the next move is to decide whether you want to keep talking at all. Keep track of whether he rebuilds the plan himself. That is the clearest sign of whether the connection is still active on his side.