Since you say losing friendships is a pattern for you-- and you've posted about it several times on this board-- then maybe you could look at what you're doing to contribute to this problem. You've said a lot of really negative things about this friend of yours, as well as other friends you've mentioned-- you've listed their faults and called them selfish, narcisstic, users, etc. Your tone also comes across as pretty negative and angry. Perhaps you come across that way in person also? Certainly, the letter you describe that you sent your friend listed her faults and your complaints about her. Maybe this pushed her away. People tend to want friends who build them up and make them feel good about themselves, rather than friends who tear them down. Sure, sometimes we need to tell people they've hurt our feelings, but that can be done face-to-face in a caring way-- talking about YOUR feelings and how they got hurt precisely because you value the friendship so much, rather than talking about what a horrible person they are or how awful their actions were.

As others have pointed out, friendships also change over time. People drift apart. People meet new friends and lose touch with the old ones. She may have drifted apart from you initially not because anything "happened" but just because time passed, she got closer to others, and was no longer as invested in the friendship. People don't usually call someone up and say: "Hey, I have other friends I'm closer to now. I just wanted to let you know that I'm going to start calling you less often. We have less in common now than we used to." It's just something that happens naturally. By the time the other person realizes this is going on, is reaching out, and not hearing back-- the drifting probably happened awhile back. The more you push someone by contacting them, not hearing back, contacting again, not hearing back, etc-- the more they are likely to avoid you and avoid dealing with the situation. I'm not saying that is the "right" way to respond-- just that it happens all the time. People don't really want to have a confrontation if they don't have to, so they do the "slow fade" and hope the other person gets the hint. Maybe she owes you a call to say "Hey, I'm not really invested in the friendship anymore. I'm probably not going to be returning future calls"-- but, honestly, most people don't make that call. They don't do it because they don't want to hurt the other person's feelings. Granted, by not making the call, they probably hurt the other person's feelings just as much. This doesn't make them a bad person, though. It doesn't really make them narcissistic or selfish or a user. It makes them someone who has drifted from an old friend and is no longer interested in the relationship. At some point, we are all that person. Just because they don't want to be friends anymore doesn't mean they were using you during the whole friendship. It means that, at some pointed, they drifted or no longer enjoyed the friendship. Now, they want out-- and are hoping the "slow fade" will work. It's just something that happens. The healthiest thing to do is to just let the friendship go and move on. Find people you have more in common with who are also looking for friends. If you find that you are struggling to make friends, maybe talk it over with a therapist. Maybe you are carrying around some negativity that is making you less attractive to others as a friend.