~Sex~
For real vampires, sex provides an opportunity to obtain large amounts of pranic energy without creating an imbalance in their partner. During sexual contact, the normal defenses which protect the integrity of each partner's energy system are greatly reduced. There is much more mixing and combining of auric energy, and there tends to be direct skin-to-skin contact between the primary energy centers (upper lip, solar plexus and groin). Penile penetration of any orifice of the body of a partner (gender irrelevant) means that the owner of the penis is literally placing his root chakra inside the body of his partner and feeding him or her pranic energy, like watering a tree with a hose stuck into the ground. It should be little wonder that many real vampires are extremely fond of sex. (Occasionally, a real vampire can't deal with sex at all -- it's just too much energy at once to handle. This can change with training.)
Although real vampires often become highly skilled sexually, they may not always be satisfying lovers. Sometimes the partners of real vampires experience unusual and inexplicable fatigue, or become physically cold to the point of shivering. Sometimes they have difficulty attaining orgasm, in part because the real vampire is siphoning off their energy before it can peak. These problems are most evident when the real vampire is imbalanced and "hungry" and has not learned how to recognize and correct for this.
Real vampires often can feel their partner's orgasms directly as a rush of energy. They may enjoy their partner's orgasm more than their own.
A one-night-stand with a real vampire can be quite an experience. Unfortunately, long-term sexual relationships with them are often fought with problems. Real vampires, not being human, often don't have the same needs, emotional responses, desires and expectations as their human partners. Eventually, this soul-level incompatibility will lead to stress, whose source can be difficult to diagnose. Even if the real vampire has done enough self-transforming work to understand what's going on and try to explain, the partner will rarely, if ever, believe the truth. The real vampire tends to be accused of being cold, uncommitted, emotionally distant and so on. Real vampires who are completely unconscious of their inner natures tend to get involved in abusive or stormy relationships that break up messily and painfully.
Vampires are not all sterile. But those how are not sterile find it difficult to get pregnant. Many first pregnancies are lost, or the children die very young, because of the medical problems.