I used to have the "Connect connect to the game session", but then I took an arr.. nevermind.
It works now.

All I did to fix it was download gameranger (www.gameranger.com):
- Created an account
- Hosted a game (BG2-TOR in my case) via the gameranger client.
- My mate joined my game in the gameranger lobby.
- I pressed start, and the game was launched.
- I was presented with the "host session" game interface, where I just had to press "New" (was sceptical at this point).
- It hosted the game as always and my mate pressed join in the GR lobby.
- He was presented with his usual interface inside the game - only difference: THIS TIME THE FREAKING THING ACTUALLY CONNECTED.

I'm not sure why it works through gameranger... maybe it performs some kind of connection mitigation - I haven't researched it.

(If you are using a mod like EasyTutu you should have your BG2-Tor profile in GR point to the new directory that Tutu creates)

Ps. It should be mentioned that we both have ports 2300-2400 and 6073 open in both our routers. Not sure if this is relevant since it didn't do us much good previously.

Pps. Things we tried that failed:
(The game is not installed in "C:\Program Files (x86)\" btw)
- Running in window mode.
- Running as admin.
- Running in compatibility mode.
- Opening above ports.
- Making sure we have the exact same mods installed (we do)
- Disabling GameSpy in baldur.ini
- Setting Cache up to 10000.
- All of the above at the same time