Unconsciously Celibate

My friends asked me again this weekend why I don't just marry D, the guy I had a huge crush on in high school, remain (long-distance) friends with today and actually tried one or two times to visit him to specifically see if the spark was there. He's the one I still consider sleeping with but know in my heart of hearts I won't because I don't want to hurt him.

They asked if I had ever slept in the same bed as him. I said yes. They were surprised. Seems I can still do that. Surprise them that is. Anyway, the first time I went to visit D, I went with the idea of a potential relationship in mind. Thus why I think I agreed to sleep in his bed. Being extremely respectful he stayed on his side until he got the nerve and threw his arm over my side. He asked if it was ok and I said yes. Mostly because I couldn't say no, but also because I liked it despite being completely freaked out and deciding that I didn't want to pursue anything. I pretty much froze with his arm over me. I don't remember much else but I'm sure I didn't sleep that night.

ISSUES!

So the spark wasn't there, nor was it the second time I visited, but I still harbor the desire for there to be. Every time I visit him or he visits me, I hope for the chemistry and at the same time know at this point it doesn't seem likely that I'll let myself feel it anyway. It's silly I know, and probably just a desperate attempt to believe that I can have the spark and the want to be with someone long term too. I dunno.

But I always come back to not wanting to hurt him. How presumptuous is that? If we got to really know one another again, by being in the same place at the same time for a length of time greater than 3 days, who's to say his crush on me wouldn't dissipate? Or mine on him wouldn't grow into love? (And I do have a crush without a spark. Actually, I have many of those. All on older men, aside from D who is my age, I think because they don't actually pose a threat and we can flirt without me having to worry about getting pregnant. Also, older men in general know how to make me feel good without coming across as only wanting to get in my pants. Though they make that desire clear as well...)

Why am I so obsessed with that spark?
And why haven't I really felt any chemistry with anyone?
Can I really do that much inhibiting with my mind?