Connecting to 2 networks simultaneously

I am currently connected to 2 networks. My router has my modem connected as source, my computer via LAN and another LAN wire going to a wifi booster that connects to my friends network.
This was done so that we can share files easily and play games via LAN without a hastle, however my computer keeps using his internet instead of mine. To change this must I change the gateway or DNS to not have his networks details.

Basically my network is 192.168.2.1 and his is 192.168.1.1, I have both details in my network center under TCP/IPv4.

I just want to use my internet instead of his.

Thanks