I don't remember if I have ever seen someone saying that Regulus Black wouldn't have a relationship with a non-pureblood because he's a blood purist, but i strongly disagree with that.
This man chose to sacrifice himself over Kreacher, therefore considering his house elf's life more valuable than his own. Which means that he made one exception for his ideas of wizarding supremacy out of love.
So if a half-blood from his enviroment had caught his attention, started to matter a little for him and eventually found a place in his heart, it wouldn't be impossible for Regulus to make another exception for someone so extraordinary that turned his world upside down.
And for me, that someone is Severus Snape. He had the most disadvantageous situation out of all the DE slytherins him and Regulus went to hogwarts with, and however he still managed to surpass every single one of them in hierarchy and as a dark wizard.
I guess Regulus Black would turn off a little of his prejudice in order to have a chance with the guy who knew more curses in his first year than most of students from the seventh year and who was creating his own spells at his sixth.
I guess Regulus Black would make an exception for someone who shows extreme devotion towards his loved ones.
I guess Regulus Black wouldn't mind falling in love with Severus Snape.












