People develop divergent interests, become engrossed in jobs or relationships that take up more of their time, all sorts of things happen to cause friends to move in different directions. Don't take it personally. I've rarely known a friendship - as in close, spending hours every week hanging out together, sharing intense personal interests, etc - to last more than about five years before other things in life intervene to put us on different paths. That doesn't mean I don't like them anymore, or vice versa, I just don't see or talk to them as much. People I used to hang out with every day ten years ago, I only hear from once or twice year now. Some of them I thought would be my closest buddies for life I never hear from at all anymore. People aren't possessions that you keep forever, and you aren't necessarily doing anything wrong. It may just be time to put yourself in places where you can meet new friends with shared interests.
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"Strange, inaccessible worlds exist at our very elbows"
- Howard Phillips Lovecraft