Well, I finally got it done. Thanks to the people who gave information. Apparently I had a bug too. It didn't work on my old route. I have to disagree with a lot of people here, on the current build you can very well leave the orc city. I have to agree with people, the ingame quest guid is often useless.
So, if you want to enter the living forest and leave the orc city, you have to do the following:
1. First of all, be of service to the orcs/mintorauren until you get into the sleeping chamber for the first time. Here you speak to the blond woman on your left, you get the reference to room A1 in the pub.
2. The next day you go to the pub and do the cleaning job. Then upstairs, the first door on the left. The lady opens the door.
3. Be at the service of the orcs/minotaurs again for several days now. Make sure to deal the orcs in the streets (blowjobs). After the fourth blowjob one drops the key for room A1.
4. Be of service to the orcs/minotaurs for a few more days until being sent to the king.
5. After this event you can use the key to enter room A1 again, and you will automatically go to sleep there. You wake up at night and can now enter the tunnel on the left in the slumbs. It leads to the forest. You can use this to leave the orc city.
Warning:
this doesn't seem to work on every route. I had a bug that didn't let me enter room A1, first.