What should I do about this situation with my fiance?

Seriously you are making way too big a deal out of all of this. The plans you wanted to make were all casual.... and he can't help it if he is on call.... his job needs to be a priority. The graduation is a formal ceremony... not a casual dinner that can be scheduled around his work schedule. Casual.... formal..... there is a difference. Go to the graduation and schedule his birthday dinner for an evening next week when he is not on call.