Usually when you send a message to someone that is not a Friend on Facebook, the message goes to a filtered section. Basically, he won't get a message notification on FB. When/If he goes to this filtered section on his own, he will then see that he has a message from you. I was just inclined to check my filtered section for messages now and found one that someone sent me a year and a half ago. Yikes! I hope this all turns out well for you.