So, I've been doing a lot of research and exploration on my own, seeing as I can longer afford to go to Therapy.

I've come across the concept of post-coital depression before, but it never sounded quite right for describing what I was going through. However, recently I learned about the concept of "Sub-drop." A phenomenon common throughout BDSM circles. Sub-drop refers to a kind of crash that can be experienced by the Submissive partner after anything from mild to intense BDSM play. This crash can be immediate or can begin anywhere from a few hours or even a day or so afterwards and can last as long as a couple of days.
Symptoms can include: Fatigue, feelings of guilt, helplessness, pessimism, irritability, worthlessness, insomnia, and worse. Unpleasant stuff to be sure.

Now, given my history of Sexual Anorexia, I obviously don't indulge in BDSM practices. I don't indulge in much of anything really.
But, in spite of that, as I read about this I couldn't help but think, "Wow. That sounds EXACTLY like me."

I had experienced all of those symptoms, to varying degrees, my entire life after indulging in my own sexual urges. Reading about this sub-drop thing was so relatable and accurate it was scary.
And seeing as I, well, don't do BDSM or, well, anything, I looked into the science behind it. It's fairly simple. During sexual arousal or activity, our bodies release endorphins. These endorphins are meant to, well, get us high! They make us feel good, they make the more un-sexy parts of sex, well, seem sexy. And once sexual activity is over, those endorphins drop out of our system.
Everyone experiences this drop to "some" degree. Some simply temporarily lose interest in sexual activities, some feel a nit bummed out, that being post-coital depression.

So, essentially, my hypothesis as to why I've always felt terrible for thinking about sex or acting on my sexual desires was more or less correct.
I, for whatever reason, experience an endorphin drop FAR beyond what one is "supposed" to experience. I basically undergo "sub-drop" after thinking or doing ANYTHING sexual. That explains the physiological side of things.
Following that, the psychological side of things isn't hard to piece together. Ever since I hit puberty, sexual thoughts and exploration has been met with this severe negative reaction. This continued my whole life. So it's no wonder that I grew to resent my sexuality, my sexual thoughts, my desires, and sex in general.

Not sure if I'm actually going to be able to actually, you know, DO anything about this. But it's oddly comfortable to know the how's and why's of my situation.