This is the face of an abusive kismesis relationship right here. Though both sides equally hate each other, one side is scathingly cruel while the other is incapable in every way to defend herself at all. His actions towards her were exceedingly heartless even by troll standards and while she knows well enough the destructive spiral the relationship is setting her on she is cannot break it off before she HATES the man's guts SO DAMN MUCH.
When we first saw Terezi hiding her eyes under her hood, I actually thought she was hiding dead eyes from Karkat, that maybe she killed herself in secret so she had an excuse to stay behind with the others and make plans. Then when her eyes were revealed, I completely misread what she said. I thought she was saying, "You know, TEREZI'S ancestor?" Then I'm like, WHAT the GLUB, why is Latula alive and why did she switch places with Terezi?!? This completely messed me up XD