I have been like this my whole life. Basically, when I get very close to someone I tend to opt out and emotionally distance myself. This is one of the reasons to why I have never had a best friend or someone I can entirely confide in. I sure have good friends, and I'm liked by my friends but I get uncomfortable if we become too tight. I feel so overwhelmed and not comfortable. Most of my friendships are shallow, except the ones where I have known the other person for over 5 years. Shallow in like, they don't know a lot about me outside of the partying/getting a coffee together/seeing each other in school.

As an example. I recently started college and have become tight with some girls in the same dorm as me. We party together and we've even had sleep overs etc. We get along great and me and this girl have bonded quite a bit, as in we can talk about everything even though we've known each other for 3 months. But now, I feel way too uncomfortable and have decided to distance myself a little. I don't talk as much with them as I did before and I give them made up reasons why I can't attend a party they are hosting next week.

I notice that I've behaved like this since I was a little kid, and maybe it could be a reason why I don't have "best friends" or people I hang out with regularly. I just don't understand how every other person in my age can form stable and intimate relationships with others while it feels so uncomfortable for me to do so. And since I'm a girl, I feel like it's expected of me to form intimate platonic relationships with other women? I feel like a freak for not being able to do so.
Some help and advice would be appreciated. I think I might have a serious issue with attachment to other people.