Hi Nnoir... Welcome to Anxiety Zone!
Unfortunately, living with another person is not an easy thing to do, under the best circumstances. The way that your roommate and you maintain your flat, appears to be as different as night and day. For roommates, I sure would consider this to be a big issue.
A suggestion would be for both of you to write down what you are looking for in a roommate. Then, find a third, impartial person who can read both of your lists, and have the three of you discuss what changes can be made.
Unless the two of you are willing to compromise, and work things out, the bottom line here is that you two just might not be compatible living together.
Certainly if things don't workout, you might have to go your separate ways. If that becomes the case, there is nothing wrong with you being selective if you get another roommate. You will already have a list of traits that you are looking for in someone to share a flat, and this will help with your selection.
Good luck with the outcome!
The very best to you, Nnoir!... Chuck