Like Jerry explained, if you're looking to handle multiple requests using a single socket you'll have to add an identifier to each connection.

Each paquet should be like this:

BUFF_SIZE | DATA | UNIQUE_ID

I just made a simple reverse proxy in C++ if you want to check it out: ReverseProxy. It uses a single socket for all the interactions between the client and the server.

It's in Spanish but I hope the code is easy to read and understand :)