The love scene was symbolic and didn't actually happen.The love scene between Dracula and Lucy is prefaced with Dracula saying to Lucy "I need your blood. I need it." It's preceded and followed with shots of Dracula biting Lucy and draining her of her blood, as if the love scene was just supposed to be a symbol of what Dracula biting Lucy in the neck and draining her is supposed to feel like. The red background during the love scene itself just adds to the blood imagery/symbolism that otherwise wouldn't be there.
WMG / Dracula (1979)