1. "all of my relationships since age 16 or 17 are people who are psychos or similar"
2. " i especially like when they're sadistic... it's stuff they're capable of"
3. "he shot a stray dog with a bow and arrow...this was the most turned on i'd probably been in my whole life."
4. "i get more pleasure out of their exploration of depraved things than my own."
5. "i like when someone is an asshole or callous towards everyone else, but intimate with me"
6. "the bigger the contrast of ow he regards humanity and how he regards me, the more good it gets."
7. "we've been on and off, mainly due to drama with his ex-wife (he's older)."
Given the fact that you've provided so many important information on your mental state and your sexual selection preferences, I think I can give a pretty accurate explanation - what is missing from the "equation" is you didn't state your biological gender (and a few other variables, by I can ignore them for the time being) - so I'll assume you are a female, probably in your 20's.
Your instinctual desire to mate with males who are perceived by others (and you, indirectly) as "psychopaths" has NOTHING to do with them actually being psychopaths (so no, it's not a psychopath fetish), and everything to do with how your instinct interprets masculinity. For the female in you, the most important biological imperative is to mate with a high-status male (aka "an Alpha") and "she" interprets status and power physically, achieved through brute force. You are, to a large degree, similar to those women who deliberately stay with their abusive boyfriends/husbands - the only difference is that the "abuse" is not directed at you, but outwards, toward those not included in your little pack of two. You perceive your "psychopath" male as the alpha-dog, and yourself as his second-in-command - which is a pretty high status - and yes, it is an ego thing. It always is, and everything is.
By no means should you associate your mental state and sexual preference with some kind of pathology - you are more sane then those other women whose mates abuse them. You are siding with destruction, they are siding with self-destruction. And self-destructive beings tend not to live long and/or prosper.