Nothing wrong with saying you want to change your appt time away from Fridays because he might get tied up like he did this time.
Why should you have to wonder every Friday if he will be able to make it?
You have needs to. Reasonable needs that include needing to be able to rely on your scheduled appt time.
My T did something similar recently but there wasn't a no show involved. My appt has been on Tuesdays and she needed to reschedule away from Tuesday because of a conflict. (No she didn't give my appt time to someone else--I asked!!). She suggested Monday and thought I was agreeing when I was just thinking. But she wrote me in and the next week I saw her on Monday. Well I didn't want Mondays at all and told her next time. She changed it to Thursday, then changed the time to 7 instead of 8 and I nearly missed the appt because I forgot the time changed too. I have told her before how I NEED a regular appt time. So when I arrived late (after calling to tell her I'd be late) I walked in and said, "SEE why I need a regular time?!?!". She just said "Yes." and it's been Thursday at 7 since.
Sheesh. They tell us to have a life outside of therapy, then think we are free all hours and days. lol. grrr.