I've always taken that Cass ending as her drunkenly seeing the Courier as just an NCR soldier after all the shit he did for them, the destroyed barracks bit and him being in seemingly the Courier's room on the Dam at night makes it a bit too specific. The timeline of the endings makes it so that the Courier later gets an award from the NCR and Cass' slide takes place right after the 2nd battle, so the Courier can't be gone mysteriously before then.
But it could also just be soft cucking, I wouldn't disagree with it going either way considering how Cass is written