AnnaBegins, it sounds like your therapist has a very loose "therapy" frame and that your sessions are very casual (in both organization and the way/places they are held). From what you say it seems like your therapist doesn't adhere to the normal professional boundaries that protect therapy and the client. His note to you about "sorry, something came up and I didn't hear from you" fits with the casual boundaries he holds. It just all seems like something he wouldn't place too much emphasis on.
So in answer to your original question, no, I don't think that is okay.
But at the same time I think your therapist probably does think it is okay. That doesn't make him right.
A more professional therapist would hold better boundaries and (hopefully) be more reliable. But you might be quite happy with the therapy this guy can give and want to stay with him. I think a therapist with loose boundaries and a casual therapy frame isn't likely to change his habits. But you can choose whether you're okay with the therapy and casualness he offers of if you want something different.