Looking for a movie that I can’t remember title of

I can’t find a movie I watched years ago. It wasn’t on a streaming platform, so I can’t search my watch history. It was about how a daughter’s military boyfriend/fiancé and her mother killed her (the daughter) then the boyfriend and mother finally got together in a relationship. If anyone could help, it would be appreciated.

Also, if I remember correctly the boyfriend and mother have sex or make-out in a car at the end.

Before I dig harder, can we rule out “intimate relations” and “texas cadet murders”?