It took awhile to figure out but after following this guide, downloading the SteamCMD Server, and double checking with a video on PortForwarding… toxicroach and I were able to play the Half Life: Opposing Forces Story Chapters together with Sven CO-OP. This acts as a multiplayer server so quick saves wont work, your health regenerates with each death, your in game character model/weapons might be different than what was intended, players reconnect with every checkpoint/new level, and glitching out in a level would mean restarting the entire chapter over again. But aside from that, it was actually pretty awesome.
*Playtime: 11? Hours (03/27/20 – 04/01/20)
*Playtime: 7 Hours 16 Minutes (03/24/20 – 03/25/20)
*Play Time: (10/04/17 – 10/16/17)
This isn’t my full playthrough as the beginning wasn’t recorded but tis the last few parts before I beat the game for the first time