There is not enough information here to make the assumption that the problem is entirely the boyfriend's fault. There is a shitload of reasons as to why this could be happening. For all we know, the boyfriend could be getting rejected when initiating sex or vice versa, they might live far apart, they might have busy lives and have trouble finding the time, either the boyfriend or OP might be trying to initiate sex with the wrong timing (eg, end of an exhausting work day or on a stressful day), the boyfriend may do it to unwind, it goes on. Nowhere in the post did OP state that the boyfriend told OP he prefers wanking over OP, the post implies that this is how it made OP feel upon learning this- there is no information to confirm that this is exactly what is going on. They need to talk about it- not train each other. Furthermore, it's incredibly apathetic to regard humans as nothing more than animals that require training- especially if it's a significant other. That's disgusting.

You had several valid points, right up until the last two sentences. Ask ANY mental health professional or physical trainer, it is most definitely possible to train ones self, and others. It's just the way we humans are. By now you have probably trained yourself into several habits, good and bad. If you think it's disgusting for me to acknowledge this facet of human existence, that's your problem. As for the apathetic part. If you actually think that, you either don't know that the word means, or don't know how to use it in a way that makes any sense.

I believe problems like these are more complex than simple misbehavior that needs nipping in the bud. Also we cannot change others- only ourselves. To me, attempts to "train" another person is willfully disrespectful and selfish- even if you're doing it for reasons that are, in your opinion, the best for that person or for their own good. To do this to another would show your apathy or indifference towards that person in the sense that you are disinterested in or lack sympathy for their right to just be as they are. And yes my disgust is my own problem and I'm not telling you that you are wrong or that you have to change your mind about it, I'm just saying it's wrong to me and I'm simply sharing ideas- just the same as OP's problem and intention through making this post in the first place.