Then he needs to use his own wireless adapter to "see" your network and enter the security key just the first time to gain access. After that, connection will be automatic.
There are downsides to doing this. If he has young children who might be into downnloading Copyrighted material, your are the holder of the IP address and would be held responsible if the ISPs are forced to take action against those practices. You might wish to have a conversation with him about this before going further. [/#000ff]
While I think it's a great idea to share your internet (especially if you have a neighbour who is mostly out while you are in) the ISP's would rather everyone paid them for their own connection.
So check terms and conditions and you'll see it's best not to mention this arrangement to your ISP. There's a possible risk to your own privacy and (as above) be aware of the wider legal implications if your neighbour abuses the connection.