I agree that this is not an issue to muck around in and make bigger than it really is. I will say, though, that what struck me was how easily you let such a small transgression throw you into thinking you're not important to him and that he has eroded your trust in him because of it. I think you must let yourself feel hurt very easily.
Let it go and give him the benefit of the doubt. Just make sure you are very clear in your communications from now on. I know SNeacail
has said that she has her husband repeat back to her what she tells him just to make sure that he heard her and understood, because they each have very different communication styles. And communication isn't just speaking - it's listening, too. You could try that, and even offer to send him a reminder via text or email, if he is the sort that forgets appointments. The thing is, if we need something from people, sometimes we have to be proactive in making sure we clear the way for it to be given to us. Then, at least, we are not victims.