step 1: download this player model https://www.gamefront.com/files/cf_gordon/;3752526;;/fileinfo.html
step 2: extract the files to your steam\steamapps\sourcemods\BMS
step 3: go to your steam\steamapps\sourcemods\BMS\CFG directory and open listenserver.cfg with notepad and change it to look like this
sv_lan 0
maxplayers 4
sv_cheats 1
sv_region 255
mp_flashlight 1
deathmatch 1
step 4: right click on your Black Mesa shortcut in steam and click on properties and then set launch options and add this line without quotes
+exec listenserver.cfg
step 5: now download tunngle or hamachi and launch the game and open the console and type in the map you want to play(the game will transition to each map from then on, just like in single-player, or possibly crash)
example: map bm_c1a0a (right after the tram ride intro)
after be sure to type ip “type your hamachi or tunngle IP address here” without quotes
step 6: get your friends to download tunngle or hamachi and connect using the console (connect “hamachi/tunngle IP here” without quotes) now have fun!
 
   
   
   
   
   
  
 
      
     I would recommend getting that and using the console while hosting a match and switch to a single-player map and cooping that way. It crashes a lot less now, mostly only when you touch a barnacle’s tongue or when a scripted event goes out of order in the map, So you have to try and not skip(noclip) over any rooms, that mean even if you crash, play it over again, each time you crash and host the game again you can’t skip any rooms and places with explosions or npc’s trying to talk to you. If you die though THEN IT’S OK TO NOCLIP, you can respawn and noclip back to where you were at.
        I would recommend getting that and using the console while hosting a match and switch to a single-player map and cooping that way. It crashes a lot less now, mostly only when you touch a barnacle’s tongue or when a scripted event goes out of order in the map, So you have to try and not skip(noclip) over any rooms, that mean even if you crash, play it over again, each time you crash and host the game again you can’t skip any rooms and places with explosions or npc’s trying to talk to you. If you die though THEN IT’S OK TO NOCLIP, you can respawn and noclip back to where you were at.