Get out, even if it hurts a little

Q. I have been friends with "Jen" for 15 years. Over the last few years, and particularly in recent months, I have come to realize that Jen is not a very good friend.

While Jen lives across the country, her e-mails are ever-present and unpleasant. If she's not complaining about some aspect of her life, she is criticizing me and my life. For example, when I wrote about an incident where I was hit on by someone inappropriate, she responded not with sympathy, but with a nasty remark along the lines of, "You're always getting hit on, but it's always by these weird guys that have something wrong with them."

I know much of what she says is a result of insecurity, but I've had about enough. She is extraordinarily sensitive and I am not a big fan of confrontation or hurting people's feelings (although she spares nothing with me). How can I either extract myself from this friendship without hurting anyone, or somehow improve it?