Fiction is just fiction, and it can be really messed up. It's very unlikely to even be a reflection of the writer's character, let alone anything else. I should know - I'm a shy person who feels horrified if I so much as accidentally step on someone's foot, and I have written some very dark stuff (though not porn).
Now, I don't know what it means that people seem to like my dark work the best, but I guess people like creepy stuff, just like they enjoy the thrill of a roller-coaster ride - you get to have certain experiences in a safe environment. Even if just mentally. It's the paradox of painful art.
The key there is that those things people experience through fiction of a darker nature tend to be things that they would never, ever do in real life. Those girls fantasising about that stalkerish vampire in Twilight would completely freak out if they met a guy like that in real life. Same as they'd run a mile from a stalkerish control freak who'd only want to be with them if they become his slave, like with the character from 50 Shades. Or the vast majority would, anyway.
My advice would be to focus on films, series and reading material that cheer you up. That may be easier said than done, I know, but when I was in a dark place mentally, it really helped. You can train your thoughts to go in the direction you want them to. It takes time, and it takes practice, but it's worth it.