The "bad" ending is just to escape the forest without doing anything special. In order to get the "good" ending, you need to make sure you've made the antidote AND given it to Dr. Stammerts before you leave. In doing so, you should also get a lot of background information about the game world and the story which aren't necessary to beating the game, but which will allow you to figure out a lot about the story which isn't explicitly told to you in the game by the characters. I'm glad you enjoyed it, and that you enjoyed it enough that you want to see the other ending! Thanks so much!