There's a lot of vitriol here, which is rather unpleasant, but I feel the need to state my opinion. Please remember that everything written below is my opinion, based off of my personal experiences.
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I really don't like Dora. I never have. She always came off to me as greedy, manipulative, sniping and self-centered. I should probably inform you that I'm a 'Faye' type girl, to the point that a number of my friends have made note of the similarities (similar issues regarding men and our fathers, similar body types, similar types of humor).
Too many times, I have developed feelings for a man, but felt myself incapable of giving him the relationship he deserved, because of an incompatibility in our lifestyles. Like Faye did with Marten, I would sit down with them and explain the situation, what I felt was preventing us from having a relationship, and an apology that because of my issues, I was unable to pursue my feelings for them. I take ownership of the situation, which is something Faye grew into with her conversation with Marten. She understands she's messed up, and accepts that she needs to fix herself before she can give the man she truly wants a fair shake in a relationship. You'll notice once that talk was over, she went and got help, started seeing a therapist.
And I have had 'friends' (though I feel that 'frienemies' is a more appropriate term) like Dora. They're strong, attractive personalities. Women with issues become attached to them, in a friendship sense, because when we're around them we find ourselves feeling braver. We think 'If I could be like that, I could deal with X' or 'I wish I had that level of self-confidence/self-reliance'. And I have gone through the situation that occurred between Dora, Marten, and Faye. When I was 19, I met a boy who I adored, more than anything. But I was just starting my therapy, and my psychologist asked me if I really thought I could have a healthy relationship - I knew I couldn't. So we had our talk. A week later, pictures appeared on Myspace (to give you an idea how long ago this was >.<) of the two of them kissing and drinking together. It hurt. Immensely. I wasn't upset with him, I wanted him to be happy. But I felt betrayed by my friend, because she knew, how I felt. She helped me work out how to say what I needed to say during the talk. She held me the night before the pictures were taken while I cried over the fact that I couldn't be with him. It was horrifying for me, I felt like the rug had been pulled out from under me. So that attributes to my dislike of Dora. When I read that story arc I felt my heart freeze up in my chest, and bad memories came rushing back.
While that heavily contributes, there is another reason I dislike Dora - she's not honest with herself, or anyone around her. Unlike Faye, up until -very recently- Dora has laid her problems at the feet of those around her. Marten's 'passivity' does not equate to being a doormat. The comic linked above, where Marten's mother demands he apologize to her, and his friends, for his behavior, came across to me as a response of emotional exhaustion. He just got out of a bad breakup in a long term relationship, and his own mother was sneaking off from dinner with him to call his ex and check on her. Arguing with people, yelling at people, being upset - those are all emotionally draining. I think, at the end of the night, the point when this event occurred, he just wanted to go home and sleep. He was done dealing with his mother, and done thinking about Dora. I think it's unfair to use that as an example of a weak self-will. Anyway, back to Dora - She doesn't take responsibility for her problems. She blames her overreactions and paranoia on the behavior of others, be it Marten, Faye, or her 'ex boyfriend' who has been referenced numerous times, and she expects her friends and loved ones to change their behavior to accommodate her.
Whereas Faye saw that she had a problem, accepted it, owned it, and didn't go bitch mode when Dora swooped in and got together with Marten. She understood that Marten's love life didn't end because she wasn't available, and though she was a little hurt, she didn't hold it against either of them.
The short version:
I don't like Dora. Dora is the kind of woman that gives women with issues a bad name.