Aye, lover is a ancient ghost and she does not get resonance even if she has feelings for someone. Abyssals are the ones being screwed.
However, sex is banned from living for this purpose; 'creating life'. So any sex which has even chance to create live (with traditional vaginal penetration example) would give resonance. That's why being sterile is actually 1pt merit than flaw for abyssals. Also positive emotions towards living person whom you have sex with adds additional resonance.
Basically any or all acts which preserve, care, create, protect or extend life of living is sin by Neverborn and worthy to gain resonance. Fucking with them while being sterile is not offense otherwise.