Sometimes people aren't able to be present. And even when they are, sometimes they second-guess their instincts and wants and needs because of other factors, like mental illness, past abuse or negative experiences, etc. If you've already encountered a predator or someone who's unhealthy for you, it messes with your ability to accurately judge situations, because on some level you might feel that you deserved the poor treatment. And that opens you up to more poor treatment.
The most important thing, in my opinion, is to recognize that it doesn't matter what anyone else says or thinks. If YOU feel like you're being treated poorly, respond to that feeling. If you're uncomfortable with the way your partner behaves, don't justify it by thinking you deserve it or by wondering if you're seeing things from a skewed perspective. Acknowledge how you feel, acknowledge that you have the right not to feel that way... and leave that situation.
You might be seeing things from a skewed perspective...but if that perspective makes you feel uncomfortable or unsafe, it's still okay to respond to what you perceive, and to get out of the situation.
The best example I can give from my own life: My first marriage was emotionally and verbally abusive. My ex was controlling, jealous, and sometimes outright hostile. It was unhealthy, and he wore down my self-esteem and confidence until in the end, the only reason I managed to leave was because someone told me Alt and Country might grow up to have marriages exactly like mine if I stayed.
About six months after I left him, I met a guy online and started dating him. He was charming and encouraging--but also hot-tempered and insulting. He made accusations toward me about other guys. He kept tabs on everyone I talked to. He blamed his behavior on being Latino, which meant I couldn't say anything against the way he acted without him making me out to be prejudiced. He knew what my first marriage was like... and he very subtly played on those fears and insecurities I'd picked up during that marriage.
But he was nice to me most of the time, and he was attractive and told me I was beautiful, and his accusations and temper weren't as bad as my ex's. Even though I didn't like some of the things the second guy said... I wasn't able to recognize it as abuse, because it wasn't AS BAD as what I'd dealt with. It still made me feel icky, but I believed that was *my* problem, not because of *his* actions. I finally got him out of my life after he found out some friends were trying to persuade me that it was an unhealthy situation--and went into the public chat room we were all members of and threatened those friends. Once again, I couldn't break it off for my own sake; I had to do it for someone else's.
The scariest thing about him was he was a social worker... who worked with children who'd been in domestic violence situations.
If I'd trusted my instincts about him to begin with, it wouldn't have escalated as it did. Hell, even now... if I'd trusted my perceptions of the declining relationship with S2, I would have called it quits sooner in a much less hurtful way than the way he quit on me, and we would probably be friends now. There was no abuse or predation in that relationship, just a whole lot of insecurity and uncertainty on both sides, but it still is relevant to my point...
No matter what the relationship is. No matter how much you think you love them. No matter how nice they are to you "sometimes"... if you feel like ANYTHING is off at all, if ANYTHING about the other person makes you feel hurt, scared, or put-down... Go with that perception. You don't have to stick it out.