You didn't really ask Niffty out, nor did she. But out of nowhere she just started treating you as her lover, kissing you and such, maybe because she saw you as a bad boy/girl? I mean, she's said many times that she likes bad . . . people, so that would explain it. Recently she's been getting more possessive, loving, and protective over you, to the point she's stabbed a succubus with a pin needle for flirting with you. Now? She's ranting about how much she loves and 'desires' you since you're a bad person... sneaking in some suggestive 'stuff'.