Vampire older woman and captive younger man

A young man has been drugged by an older woman he was visiting...she is a vampire and drinks blood. She has drugged him, bound him to the bed (wrists and ankles at each corner so that his legs are wide apart) and of course stripped him naked. She waits until he wakes up and then shaves him between his thighs until completely smooth, caressing him and teasing him so he is 'almost' on the verge of an orgasm. Every day she comes into the room and pleasures him with her fingers...and long fingernails. She punctures him with a large needle and slides it into him to draw blood...sometimes into his groin...his thigh...sometimes straight into his long thick engorged shaft.

The woman starts to have sexual feelings for the young man and decides to no only 'use' him for sustenance but to act out her sexual fantasies on him...some are very dark and deviant.

For this story sadly you have to explain some of the mechanics of your vampires and the emotional state of this woman. As it stands sadly this story doesn't make a lot of sense. Here's why.

As you've described her she doesn't seem particularly "evil" in the grand scheme of fictional evil. If she can glamour/hypnotize him why not just do that? It less messy.

If she can't why not kill the kid? A missing person is at best slightly better than a dead body. A missing person they keep looking a dead body they've found. Is she some kind of good guy vampire?

If so is she not pretty enough to just convince guys to give her a bite every now and again? Is that why she keeps him?

Why was she sired an old lady anyway? Or do vampires age here? (I would highly reccommend "Love at First Bite" staring Jim Carrey if you've never seen it. That could tie this all together nicely)

What about the boy. Is he a bad person who thought he was taking advantage of an old lady and we're not supposed to feel sorry for him or is he an innocent who happened to be at the wrong place at the wrong time?

Not important, but where does this guy go to the bathroom? I couldn't keep a sexual slave if I had to clean up after them, especially if I was an immortal vampire.

Possible sexy servants that end in naughty results? ... haha