Hi, thank you so much for liking it sooo much that you want to replay it! :D
If you want to reset the game, try skipping through the broken endings (press ctrl to skip, you can change skipping from seen to all in preferences) You don't need to see them all, just reach the last one in a similar way to how you reached the part where you could chat with Sebastian. Once you reach that ending, the game should un break itself in a similar way to how it got 'broken' in the first place, allowing you to start anew.
If that doesn't help, feel free to post again and see if you can access the .rpy files. I'll tell you how to manually set the persistents back to the starting position.