If Snape can bottle FAME brew GLORY and even put a stopper in DEATH ....

*huge sigh* Towards the end if his time at Hogwarts, Snape took the Mark and joined Voldemort. Years later, when he heard the prophecy at a keyhole, he took it to Voldemort. This much is fact. After Voldemort heard the prophecy, he determined the "Chosen One" to be Harry. Snape then switched sides, on learning that Lily and her family were in danger. He became a spy for Dumbledore "at great personal risk."
Thus, in approaching Dumbledore with the problem, Snape did all he could to save Lily. His actions, at the very least, bought the Potter family some time.

If he had saved Lily,there wouldn't have been a story.It's obvious.

Because he thought she was salama in hiding.

Because an antidote puts a stopper in death, yet it doesn't protect wewe from the Avada Kedavra curse.

I agree with all of wewe but maybe...he was just exaggerating...who knows?

The potion which can stopper death probably needs to be taken when the person's dying, and won't work if fed to a corpse. Also, it's possible that it only stoppers certain deaths, e.g. illnesses.