A brainy, awkward young American moves to England to attend Oxford University. She befriends a much older (historically heterosexual) female English professor. Over the years, their relationship evolves from one of protective friendship to something romantic, highlighting the difficulties and joys of age gap, lesbian relationships. 1,914 pages.
(This work is complete and will be posted in chapters.)
(I'm not sure if this would count as Mature or not--it's borderline in some places later on, so I'm marking it so, just in case. It's certainly not HBO in here.)