Why Is Bellatrix Lestrange In Love With Tom Riddle If He Is Half-Blood?

the last 2 films of Harry Potter i have noticed something why does Bellatrix Lestrange love Tom Riddle (Voldermort) when he is a half-blood isent the Black/Malfoy/Lestrange family all about blood purity dont they pride themselves on being a pure-blood family to why does Bella love Voldermort when he is a half-blood its the same with former Hogwarts Headmaster Severus Snape Bella and her son-in-law are freindly towards him and he is also a half-blood in reality Salazar Slytherin was a pure-blood evil manic who thought that muggle borns and half-bloods had no right to be at Hogwarts i am sure he will be shamefully discusted that his heir is a filthy half-blood i mean Voldermort himself is a hypocrite he is a half-blood and yet he trys to purge Hogwarts of all muggles and half-bloods when in fact he is one of them i just think they should of made Voldermort a pure-blood that would of made sense