I got caught up at work and was a no-show at my therapist's office. She called me right away (I had never missed an appointment in over 8 years at that point) the genuine concern in her voice was so touching. Her office is less than five minuets away, so I quickly drove over and made most of my appointment.

I would talk to your therapist about the reasons you weren't contacted, and let him know how you felt. I think that if you don't bring it up your resentment will start to build up, best to make it a topic on your next visit or sooner if that is possible in your case.