Hi Lissie,
Can you just clarify.
Has he lost wireless connection to the router
Has he lost connection to your machine whilst on his
Do you have a wireless transmitter on your machine? I have one but I've rarely ever seen anyone else with one.
I'm assuming that you have a wireless router and that each computer connects to it.
As you can see from this picture, computers connect to the wireless network independently. Then they talk to each other over the network they have established.
Once we can work out which part is broken I'm sure we can help fix it.