The sad part about the situation was that Alessa knew that Blythe was right. Sal would never care about the pain that he caused Alessa; he was a monster, and Alessa should have realized that long ago. Actually, Alessa KNEW that he was a monster, but in many ways, he reminded her of her own mom. Offer just enough good will and affection, and then strike. There wasn't even that much difference between Sal and Dahlia (Alessa's mother.)
"That's why I don't intend on telling him what happened. If he figures it, fine then, if not, great." Alessa said, as she smiled at Blythe.
Even if Alessa had lost one "friend" (who was never even one to begin with) she figured that at least she still had Blythe as an actual friend.