if your message that you have sent does not appear in the sent box does it mean he has blocked me. thanks for your help.

It means:

a) if you are not blocked, it has either been deleted unread by the recipient, or deleted after reading by the recipient.

b) there was a 'sending' glitch and the message got lost en route.

c) when you tried to send it you got a page showing : -( : -( : -( which means you are blocked and the message does not appear in their inbox.

or d) the recipients profile has been deleted.

yes your blocked!

Or was killed by the Cybermen: "Delete, delete, delete"...!