The Course of Honour is original m/m sci-fi romance posted on Archive of Our Own. It has a word count of 117,499.
Warning: one of the main characters was in an abusive relationship prior to the beginning of the book - mostly emotionally abusive, but a little physical.
Review:
The Course of Honour stars Prince Kiem of the planet Iskat and Count Jainan of the planet Thea. Five years ago, the Theans sent Jainan to marry Iskat’s Prince Taam in order to secure an alliance. A month before the start of the book, Taam was killed in a flybug (personal aircraft) accident. Kiem learns to his horror that, according to the terms of the treaty, Jainan must remarry and he’s been chosen to be Jainan’s next partner. Jainan’s certainly attractive, but Kiem has never even spoken to him before. Plus, Kiem figures he’s probably still grieving. Not that he and Jainan have any say in the matter - the marriage is scheduled to happen tomorrow.
Right from the start, their marriage is complicated by assumptions and secrets. Jainan and Taam’s marriage wasn’t nearly as solid as they’d led everyone to believe, and Jainan is sure he’s in for more of the same from Kiem. Kiem, meanwhile, just wants to make things as easy as possible for Jainan.