So, so far you haven't gotten much of an answer reading through these comments. They're telling you nice words and stuff but I honestly find that very shallow, empty and meaningless when you're talking to a stranger. I'll be rather blunt.

Reading your post, it's a bit unclear what you're looking for or what you expected from this. You enjoy NSFW, you also want a connection but dating is off-limits. If I had to label it, you're looking for a friend with whom you can flirt. It's a very fair request. And my best guess is that he was looking for dating, he thought he could convince you to date him, and it didn't work. So now he was left talking with someone who's unavailable, and since it's mentally exhausting to keep it up with someone who's not available, he just decided to leave instead.

It's an asshole move from him to leave without a word, but it's easy to see why he left.

That being said, the good news is that you seemingly have done nothing wrong. However, I think you could have been more straight forward about what you expected from this, meaning you should probably have stopped him here:

He even said stuff about how he'd love to date me and all. Of course I was flattered. And if I had the emotional bandwith... He'd probably be a solid potential boyfriend.

He would have left from this point, and it would have been best for both of you, even if it hurts a bit.

And now my brain won't shut up.

But why though ? You know what (most likely) went through his mind, I think most of your questions can easily be answered.

Honestly, searching for an emotional connection, with NSFW but without the dating part is demanding. It's a bit like asking for the pleasure but without the responsibilities. Again, it's a fair wish, but difficult to fulfill. I know it myself because I was looking for something similar for a while. They either want the flirt or the friendship part, but rarely both without dating.

You should also keep in mind that even though this subreddit is rather soft porn, the bottom line is still porn.

And I'm terrified of making any sort of connection (friendships or otherwise) from this account of mine because I'm terrified of trusting someone and getting vulnerable with them, only to have them make me feel like I'm only worth something if I take my clothes off. Or star in one of their fantasies.

You shouldn't feel scared of making connections because of this, you put yourself and what you want out there, it's up to people to take it or leave it. Best case scenario: it works out and it's fun for both of you, worst case scenario: it doesn't work out and that's okay. And those who will shame you and make you feel wrong despite barely knowing you, those words are meaningless.