His last memory of his son is seeing me through his rearview
He works with the idea of how when you see something out of a rear view you are leaving them, like a son leaving a father for college. In this case, though, it is the father leaving the son.
He’s also looking back at them through his rear view while driving away from them.
To help improve the meaning of these lyrics, visit “Goodbye” by Slaughterhouse (Ft. Ida) Lyrics and leave a comment on the lyrics box