They think all she did to little Jeremy Gilbert was feed on him.
They are so very wrong.
Of course Katherine drank from him: she was stuck in a tomb, for the love of god. She was more than thirsty or hungry. She was starving, and he was there, slow even for a human, just about as stupid as she'd quickly learned the Gilberts could be. Katherine doesn't know or care why he went into the tomb alone, but she would have expected something more challenging if Stefan was involved in the planning.
Having Jeremy Gilbert offered to her on a silver platter wasn't much fun at all, so she was forced to create her own fun.
Katherine may be weaker than usual and locked in, but she's old and experienced. She can compel the hell out of anyone, tomb or no tomb.
It is what it is: she is easily bored, and she can't be particularly picky about who she gets to misuse, abuse, take advantage of when the chances are so few and far between. Jeremy Gilbert is as good as anyone, and better than some: here's someone the Salvatores care about, each in their own way. Here's someone who'll make it out of her claws alive only to indirectly hurt Elena and even that witch afterwards with all the worst tales Katherine will let him remember.
Jeremy Gilbert honors their dates. He doesn't deserve props for it; he's compelled to come to her, after all. But it's no fun if he's a ghost, and all the advantage she needs is a taste of his blood before she lets him snap back into reality.
The first time, he struggles. He tries to run away.
The second time, he struggles, but his feet stay put. It's almost like he thinks she'll get bored and leave him alone if he stands stoically through it. It's inordinately stupid: she'll take her time either way, and he should know that. There are days between his visits, and she's thirsty every time, but she doesn't want her sole source of blood to die. She savors him.
Besides, she lets him remember where his time and his blood went, why he feels dizzy when he returns home. She doesn't let him tell anyone, but he's well aware he's been here before.
He starts making noise on his third visit, these delicious yelps of pain that turn into shouting. She puts her hand over his mouth and he bites her, hard enough to draw blood. It colors his mouth, his nose, his chin. She doesn't know if he swallowed any; she doesn't want to know. It would be tempting to turn him, just for fun, and she doesn't want that temptation. She wants him human, warm and active and full of life.
In the hours after his visits, she plans her bites: she mixes up the spots, tries to make them easy to hide. Compelling someone to lie about his wounds is more effective when those wounds don't fall on places commonly exposed. His neck is off limits, and so are his hands. She does the inside of his elbow twice, and low on his collarbone.
The fourth time, he falls down on his wrists, and she pounces on him while he's still down, twisting his arm in a way she knows won't injure him. She laps up the blood that's pooled down his forearm first; he complains, struggles to get out from under her, but his moves are all wrong, the sounds he makes are all wrong. She narrows her eyes and watches the side of his face as she sinks her teeth into the sweet veins of his wrist, and the noises become even less of a way to channel the pain.
He closes his eyes, which isn't new in the general scheme of things, but which she's never seen him do this early or this softly, and his mouth hangs a little open, differently from the way it does when he screams. A grunt comes through his noise, and then he presses his lips together, tight, like he's trying to hold something in.
She knows it's not a cry for help.
She keeps drinking. He keeps pretending she's not getting a rise out of him.
This time, this is all she allows him to remember: the way he felt when she was drinking his blood, the unconscious roll of his hips between her thighs, all the moaning he bit in.
The next time he comes back and snaps back into reality, he doesn't even bother to struggle. She knows it's not giving up by the way his eyes gleam when she drops to her knees and undoes his fly. It's giving in. It's better than if she'd compelled him to like this.
She bites the inside of his thigh, the soft skin higher up, and she's close enough to him that she doesn't even need to use her eyes or even her nose to know he's getting hard; she can feel it on her cheek, through the fabric of his briefs.
She drinks leisurely, and brings a hand to rest up on his hip. What would have been a screaming nightmare three weeks ago is now little grunts and groans and the clacking of his head against the wall. She looks up and licks her lips when she feels satisfied, and she gets a kick out of watching his eyes shut down, his nose scrunch up.
"Katherine," he says, and it's not addressed to her. She knows it isn't.
"Yes?" she says smugly, dragging her hand over his erection, squeezing lightly through cotton. He glances down again, and shakes his head, and she can't believe she hasn't exploited this before. It's so simple. Stroking him absently, she says, "You're just fascinated by vampires, aren't you? Do you enjoy being my meal?"
"Shut up," he says, like he has a right to, and she laughs.
"You're going to have to do better than that." She pulls him out of his briefs and lowers her mouth onto him. This is fun. It's much better than letting him remember he got a handjob from an evil vampire. It's better than letting him remember he enjoyed it. If he looks down right now, he'll have the image of Katherine's mouth wrapped around his hard cock for as long as he lives.
The thing about images is they're not filled with personality. If two people look the same, it may be hard to tell them apart. And she looks exactly like his sister.
Playing with Jeremy Gilbert just became a lot more interesting.