After the Spector-produced and Weil and Mann-written You've Lost That Loving Feeling, and after producing the Weil and Mann-written (You're my) Soul and Inspiration, Stand By was Bill Medley's attempt to do the whole thing himself: write, produce, sing (w/o any help from Hetfield). It's the same (force 9 gale, melodramatic) song and performance again, only this third time through impassioned, abject masculinity, the leavee's lament is from an even more pathetic perspective: not a current-leavee but a past-leavee who's stuck in the past ('I'm not her man, I'm just her standby/...So I'll pretend her love is mine'. Interestingly Medley swallows many of the 'her's so that, in particular the key line ends up mostly sounding like, 'I'm not a man, I'm just her standby' which is more self-lacerating and somewhat less pitiful.
The song's pathetic perspective reminded me of Mad Men's Pete Campbell (brilliantly played by Vincent Kartheiser) esp. in the wonderful Season 5 episode, Signal 30, written by the late, great Frank Pierson and splendidly directed by John Slattery. In the ep. Pete flirts with a high school senior (Amanda Bauer) in Drivers' Ed. and gets punched out by Lane. Signal 30 is set in 1966, the year when the album Stand By appeared on was released.