Your fetish is the result of Pavlovian conditioning. You may or may not be familiar with Pavlov's research. He famously conditioned dogs to associate the sound of a bell with being fed. He then demonstrated that even if those dogs were not fed, their stomachs would still secrete digestive juices of the dogs heard a bell. Remember, bells have no natural connection to food, this is an entirely artificial connection that Pavlov was able to create simply by ringing a bell just before he fed his dogs.

Sex is not unlike that. You have told us that your first ejaculation happened when you were masturbating to a youtube video of a teddy bear getting destroyed by high heel boots. At that point you began to form an association between sex and the destruction of teddy bears by women (you don't mention that a woman was wearing the high heeled boots in question, but even if you saw only boots and did not see a woman, you must have imagined a woman to be wearing the boots - after all, something about this video struck you as being sexual). And then, at every subsequent time you fantasized about this particular kind of event, and experienced an orgasm, that reinforced the fetish. You were effectively training your brain to associate sex with the destruction of teddy bears by women - even though that was not your intention, you were just masturbating. But masturbation is a powerful form of conditioning.

To explore slightly deeper into the origin of your fetish, I would infer some degree of masochism on your part. A dominant woman, technically known as a dominatrix, is usually imagined to wear high heeled boots. The high heeled boots are part of the sexual fantasy. Just as they can destroy a teddy bear, so can they also inflict pain on a submissive man. It is much more painful to be stepped on by those pointy heels, than by regular type shoes or bare feet. While at the same time, high heeled shoes are also part of elegant female attire. As footwear, high heels are massively inefficient. It is much harder to walk in high heeled shoes than in regular shoes. Women wear them only for reasons of fashion, as they wear lipstick on for reasons of fashion. So if a woman wears them it is a statement that she wants to be sexually attractive. This makes her, to some degree, a sexual object. She is announcing her sexuality. Si you have that combination of sex and danger, presented by high heeled boots. The woman who wears them wants to be sexy, but may also step on you. So that connects to sado-masochistic fantasies.

So you already associated the boots with a sadistic female, and so you were prepared to create a sexual fantasy when you saw those high heeled boots being used as a weapon, on youtube. The fact that the victim of those boots was a teddy bear was purely accidental. The teddy bear does not inherently have any sexual content. But now you are conditioned to think that it does.

It is likely that you are already conditioned to the point where this is always going to be a part of how you think about sex. It also is not really true that this is something that could never be incorporated into sexual intercourse. Some accommodating woman might very well be willing to perform this act for you, as a prelude to other types of sexual activity, or perhaps even simultaneously with other types of sexual activity - that may sound complicated, but I can assure you that I have seen more complicated forms of sexuality than that.