What do these lyrics mean?

Salt is know to kill vegetation, like he killed the relationship.

Aqua seafoam shame-drugs

Sunburn and freeze burn sounds pretty damn painful, like their relationship breakup.

Choking on the ashes of her enemy means despite conquering previous demons, the couple is still feeling the effects of said demons.

Eh eh?

Nice interpretation!

I picture Kurt as more of a free-form/stream of consciousness writer. In my experience writing lyrics, sometimes you honestly just write down what's on your mind and make sense of it later.

I thought it was "choking on the ashes of a runaway"

oops.

I'm no Nirvana expert, but I'm pretty sure "Aqua sea foam shame" is "I'll proceed from shame" and "sunburn with freeze burn" is "sunburn with freezer burn."

It's about his marriage to Courtney Love if I'm not mistaken. I guess "find my nest of salt" could be taken in a number of ways, but given Cobain's deep depression, I'll assume it means that he'll make a home out of (a) his tears or (b) a substance that exacerbates the pain from wounds. In other words, he'll endure the shite that Courtney Love is putting him through. "Everything is my fault" is obvious. "I'll take all the blame" is obvious. "I'll proceed from shame" means that he'll be the one to get over the shame that results from his arguments with Love. "Sunburn with freezer burn" means that Love has burned/hurt him in every way. "Choking on the ashes of her enemy" is a play on the "burn" image from the previous line and, I suppose, suggests that Courtney Love will choke on him being the bigger man?

I don't know. That's the only sense I can make out of it.