Rooms have an Ethernet port for each resident sleeping in that room to connect one machine to that port. For example, a typical double room in residence halls has two ports for each residents computer. This mean that residents do not need to share a port.
Even more important, sharing a port is not allowed for network security and to protect each person on the network. Since each port is assigned to the one person who requests that connection, that person is responsible for any Internet or other activity occurring and can get in trouble for things their roommate is doing. Therefore, it is imperative that roommates use the correct port they request to be connected. In short, no, roommates cannot share ports.