I hate his female friend. Am I justified?

Okay, so here's my dilemma. My boyfriend and I have been on and off for the past few years. The last time we broke up was about two years ago. I left him because I thought I was in love with someone else and the person that I left him for ended up cheating on me. We've been trying to work out our problems and have recently moved in and adopted a puppy together. The problem is that he has the female friend that I hate. I had met her prior to the last break up and was very vocal with him about the fact that I didn't want him hanging around with her anymore. He continued to see her despite my objections. After we had broken up, I got into a serious relationship with my ex, and this was the first man that I had been truly faithful to only to end up being cheated on. I realized I messed up and wanted another chance.

During this time, he had mentioned that he was seeing another woman but was unsure if it was going to go anywhere. He later admitted that he thought he was starting to fall back in love with me but he wanted to keep our relationship a secret because he wanted to let the other woman down easy. I question him about it and he tells me that she was the other woman, that he had caught feelings for her during my absence and they were starting to date before I came back and he thought he was in love with me. And the feelings were mutual. I told him to cut her off, but she eventually ended up cutting him off after seeing I made our relationship facebook official anyway. The problem is that now, he talks about her all the time. Most of our fights are about her and when we're not fighting, he's always mopey and depressed and I know he's thinking about her. He says he loves me but his tone always sounds bitter and resentful towards me. He's the love of my life, even though I was too stupid to see it and now our chances of fixing things are ruined because of her. Nothing I do seems to make him happy anymore. Is it worth fixing?
I hate his female friend. Am I justified?
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