Taking the idea that Jon struggles to cum and running with it:
Jon masturbating, the testosterone he’s on increasing his libido but he still struggles to achieve orgasm. Beginning to fantasize about Elias. He’s so…. so sure of himself. So steady. So authoritative. What would it be like if he caught Jon masturbating? Saw how badly he was struggling. Rubbing himself raw, fingers pushing inside, pleasure building and building and building but never going anywhere… his father taking pity on him. Shushing Jon when he panics about being Seen masturbating, his dad seeing not just his glistening cunt, the hand rubbing at his cock, the tight pucker of his ass, but that Jon can’t even do it right.
And Elias being so calm, so patient. It’s alright. He knows what his boy needs. Stepping between those spread legs. Pushing Jon down when he tries to leave. Jon wants to kick him, to shove him off, but then Elias is reaching down and rubbing at his cock just right, exactly like Jon needed. Jon helpless as his body reacts to his father’s every touch, the fingers sinking inside his empty cunt. Elias who knows what he’s doing. Warm, steady hands bringing Jon pleasure, and soon enough his cunt is clenching down on his dad’s fingers as he cums and cums and cums.
Shaking and trembling through his orgasm, thinking that’s the last of it, but no. His father wants this lesson to stick. Needs Jon to learn. To pay attention to how and where Elias touches him, what brings him the most pleasure. And Jon tries. He really really does. But as the session goes on longer and longer and he just keeps cumming he just becomes less and less able to focus on anything besides how very good he feels. Elias noticing how glassy Jon’s eyes are, how he barely even responds to Elias anymore. And Elias himself is hard, of course he is, seeing his beautiful boy all pleasured and thoughtless and desperate, that greedy cunt eagerly swallowing his fingers. And so Elias decides that perhaps he should give it something else. Jon getting him all worked up, not even appreciating what Elias is trying to teach him? Maybe he should do something for his father in return. Maybe he’d take better care of himself, if he was all heavy and full of new, fragile life.
Jon’s too weak to stop Elias from thrusting deep inside. Barely even aware of anything beyond the stretch, the way his father’s shaft rubs so perfectly against his sensitive inner walls. All soft and confused as Elias begins to breed him, fills his womb with seed, Jon cumming so easily on his cock.
It’s shameful, it’s disgusting, it’s so tantalizing that it’s almost always enough for Jon to (eventually) cum on his own.
There are also sequels. They basically always involve Jon failing to masturbate “properly” and Elias catching him and realizing he hasn’t learned yet. Sometimes Elias makes Jon show him what he’s learned, touching himself beneath his father’s watchful eye. Elias calmly correcting him, adjusting the position of his legs, his fingers, before giving up and doing it himself. Chiding Jon for struggling, for needing his father to guide him through this. Sometimes Elias simply catches him again, takes pity on him and shows him what he’s doing wrong… he revists them almost as often as the first scenario. And no matter how wrong they make him feel he can never resist thinking of them in those private moments when he needs to just unwind and cum.