Who is Sarah's boyfriend?

Hint 1 of 13:

The first clue you can find is in the dressing room.

Hint 2 of 13:

Did you look at the stain on the door?

Hint 3 of 13:

Someone would have to be pretty tall to put a mark that high.

Hint 4 of 13:

Another clue can be found in Sarah's apartment.

Hint 5 of 13:

The rugby sweater in her laundry will tell you where to look for him.

Hint 6 of 13:

He also bought some perfume for his girlfriend.

Hint 7 of 13:

The person who sold it to him may be able to help.

Hint 8 of 13:

Well, if not Belle, try her employee.  (Another question tells you how to
talk to her.)

Hint 9 of 13:

You should learn the brand of cigarettes that he smokes.

Hint 10 of 13:

Did you also know that Sarah went to the opera to watch her sister?

Hint 11 of 13:

The opera owner will have some information for you once you prove that you're
in the right place.  See the previous set of hints for more help.

Hint 12 of 13:

She will eventually tell you that the man's name is James.