Gmail – How to know if I am blocked in Gmail chat

You most likely set the chat with him to be off the record.

Chats that have been taken off the record aren't stored in your Gmail chat history, or in the Gmail chat history of your contact. You and the person you're talking to can both see when a chat is taken off the record, and you'll be notified if off the record mode is disabled. Your off the record settings will apply whenever you chat with this person, until one of you makes a change. Additionally, chats sent through orkut are never saved in chat history.

That assuming that both of you are Gmail users with a Gmail username, not AIM users using Gtalk.

Chat history is only available for users with a Gmail username.

Without using a webmail form of some sort, this really isn't possible, since email is direct traffic. It's just like with snail mail, once its in the mail box, its going to its destination without hesitation or question.