I'm here seeking advice about sexual stimulation. I am a 21yo male, and have a sexual fetish. It isn't normal, and I'm too embarrassed to talk with a parter about it. When I masturbate thinking about it, I get very turned on and have great orgasms. I've been doing this for about 6 years.
Sadly, when I am with a partner and try to have sex, I often have trouble maintaining an erection. I am at the point where I rarely strive to form relationships, because failing to have sex always leads to anger and depression. The prospect of sex simply doesn't get me hard enough. Because of this, I believe I also have performance anxiety

Over the past few years, I have trained myself to become more aroused by sex. I started by watching porn that relates to my fetish, and then switching to regular porn before orgasm. I am now at the point where I can watch completely vanilla porn and achieve orgasm, but it still can't do what my fetish does. I don't get very hard until right before climax, and it takes strong focus to even get to that point. The orgasms also tend to be not as good. The prospect of sex simply isn't very stimulating to me.
I was hoping that those who have been through similar situations could give me advice on the matter. What about sex is so stimulating to you? Are there techniques that are useful in hastening this process? I really do believe in myself, and the progress I have made so far has been very encouraging. I've just been stuck in a bit of a rut lately.
Thanks!! All I want is to lead a normal, fulfilling sex life.
p.s. I am not interested in talking with a partner about my fetish, or trying to incorporate it into sex. It is really embarrassing to me, and talking to a partner about it is my worst-case scenario.