Thoughts on if Snape had made a horcrux. Like to start over new and still look after Harry if Volmort found out he was a spy?
“Dont be shocked, Severus. How many men and woman have you watched die?”
“Lately only those whom I could not save.”
“And my soul, Dumbledore? Mine?”
To make a horcrux you need to murder and perform a horrific ritual (JKR said it made her editor sick when she described it) that will tear your soul apart. Severus did not like killing, he hesitated before killing Dumbledore and was absolutely wrecked when he went to Grimmauld Place after fleeing Hogwarts. He was angry, miserable and mutinous when Dumbledore asked him to spare Draco the task of murdering him. He did not enjoy seeing people die in the least and he tried to save as many people as possible. Not only that, Severus was very concerned about his soul. We know from Voldemort that making horcruxes changes you physically and spiritually. It’s an extremely evil piece of magic that even young Severus wouldn’t touch. There was no way he would make a horcrux, not even to help Lily’s son.
If he did though, I really doubt he would succeed. Severus became a double agent out of remorse. A horcrux can be destroyed when the maker feels genuine remorse. To continue his mission Severus must deeply regret causing Lily’s death otherwise his motivations to save Harry wouldn’t be as strong.
Most importantly, if Voldemort ever kills Severus then Severus would become incorporeal. Then he would need someone else to perform a dark sacrificial ritual to build his body back. Who opposing Voldemort would actually do something like this?
Honestly though can you imagine how freaked out everyone would be Severus would go that far just to save Harry? Voldemort wishes he had that kind of loyalty. It would be one thing to kill for someone, it’s another to destroy your soul and all the side effects that come with it for someone you’re not even related to.