I want my boyfriend to pay for the dentist appointment he made me miss.
Can you tell me more about what happened?
He made me take him somewhere out of town and promised we would be back on time.
It's understandable to be angry that he made you miss the appointment. He should have gotten a ride from someone else, or taken care to make sure that you could get back on time.
It's his fault. I want him to pay for the missed appointment.
I think you are right to want your boyfriend to compensate you for what has happened, however, you should be fair to him, even though he was wrong.  You shouldn't expect him to pay for the appointment itself, but only for any cancellation fee you endured, and the inconvenience of rescheduling.