How to break up with a friend?

Just so there is no confusion, I am female (hint: my name “berry_lips”). I’m very social and have a lot of friends, men and women. And I think I’m a pretty good friend; at the very least, I know I try very hard to be one. Recently, I’ve been feeling weird and mean, but I haven’t really been able to verbalize it. I guess, I can try writing it. Here goes: I have a female friend. We’ll call her “Julie.” I met Julie two years ago at my old job. We both liked similar things and I was new at the office and was trying really hard to make friends. As it was, the soil was fertile for a friendship to blossom, and one did. It didn’t take me long to notice, however, that Julie was very negative and had a low self-esteem. Yet, I overlooked these flaws, because, despite these flaws, I enjoyed her company. In a way, I felt like I did her some good; like I was the little ray of sunshine piercing through her thick veil of negativity. Then I started noticing something else: Julie was the biggest flake I had ever met! Yet, I attributed her flakiness to her collossal family problems. Fast forward two years and many new friends… and a party at my place on a nice, hot Saturday afternoon. As I frequently did, I invited Julie. She promised to come and even called the morning of to ask if she could bring anything. When I couldn’t think of anything, she went as far as specifying what she would bring. A mutual friend, Mark, was to pick up Julie at her apartment for the party at my place at five o’clock. Mark arrived at six and was irked. He said he went to Julie’s place and rang the door bell multiple times but Julie never answered. He called her but she did not answer. Her car was in the parking lot. Julie had not call me to say she was not coming. However, given her flaky history, neither Mark nor I was too concerned about her. Sure enough, three weeks later Julie called me and left me a message: “Hi, it’s me! Just wondering what you’ve been up to. Call me.” I didn’t. And I haven’t. I’m pretty sick of her flakiness and, frankly, I no longer want to invest in our relationship. I guess I feel weird and mean because I feel guilty for ignoring her and for no loner inviting her to events, which I know she finds out about through our mutual friends that I do invite. Like the event on Wednesday. My friend, Kevin, said to me, “Hey, I didn’t know you didn’t invite Julie. I told her I was meeting you here and she said you didn’t say anything to her. She seemed bummed.” I guess I also feel weird about all this because I’ve never “broken up” with a female friend before. Or a friend – period. Well, at least I haven’t done so since the first grade. I’m very experienced breaking up with men, but this…this is different. I guess now I kind of see why men hate breaking up with women – the thought “what if she cries” even ran past my mind. Silly, huh? I sense an e-mail from her soon and I don’t know what to say. I think a formal break-up is too weird, but I also hate ignoring her, which is what I’m doing. She won’t go away either, so I’m not sure how to make this easy. Ugh! What I just said (or, rather, wrote) sounded very similar to a story my friend, Taylor, was telling me about a girl he met at club…the whole “she’s not making it easy…she won’t go away” deal. Okay, so I need to shut up now, because the whole point of this is for me to listen (or read) to what you have to say. So, please tell me…how should I tell my friend that “it’s over”? Thank you.