There is any number of reasons why he wont eat! First, check water parameters! You should be monitoring everthing(nitrates, Nitrites, ammonia, Ph, Salt, etc...) if there has been any change for the worse, the fish could be stressed and wont eat.
Second, when you said rock, I guess you mean Live Rock? If so, LR has all kinds of live on it that will naturally feed your fish.
Third, maybe the Coral beauty is eating the food after you have quite watching.
Forth, did you change his diet? If so, go back to what orginally worked. I don't know if you can get this type of frozen food, by Prime Reef is great for all fish and that is what I feed all Mine(angels love it).
Even though you saw him eat for the first 2 months, dosn't mean you will always get to see him eat. Relax, unless you see him getting skinny or acting as if sick, then worry.