Younger Guy with Erectile Dysfunction

I am 28 now, have been sexually active for the past 8 years, and have had Erectile Dysfunction the entire time. My ED appears to be independent of drugs, alcohol, fitness level, and stress in my lifestyle (I have used drugs on occasion, but have not very often). The thing most worrying to me is I am unable to respond to anything but direct mechanical stimulation- I do not respond physically to porn, visual stimuli, and I never fantasize. This is despite the fact that I wake up with an erection and can achieve one (by direct stimulation) to masturbate. The only time I ever remember achieving an erection through purely mental stimulation was when I was 14, and a female friend jokingly suggested we have sex. I have tried to fantasize, but have found that I am completely unable to imagine sex, like a mental blind spot. I lose interest very easily; for example, I will lose my erection if I give a girl oral. I have a big problem with this, as I often cant achieve an erection unless I receive oral, and I feel it is unfair that I cant return the favor. This problem also makes me a boring and unadventurous lover; I cant become aroused by role play (I hate it), see no point in sex toys, am disgusted at the thought of a threesome, and am completely unable to understand most men's fascination with lebian porn (ewwww). It's not just me I'm worried about; it's really unfair on any girl unlucky enough to get in a relationship with me- my lack of imagination makes me seem like a very boring, infrequent and selfish lover. Is there any explanation for the fact that a young guy like me has such a poor sexual imagination that I have ED? Please help.