I think I've always held out this desire, even if I'm not always aware of it, for that "one friend". You know what I'm talking about? That one friend with whom you can do everything, call any time, talk about anything. The one who will always be there, no moving, no taking back burner to the newest flame. One with whom you agree on most significant things, with whom you really identify, and who complements you in important ways. And it'd be great if they're a cuddle buddy, too. Hm....OK, so maybe that's a "spouse" or "life partner", but even in that context, I actually think it's a fantasy relationship.
And if you think you have it, it may actually be what we refer to as "codependence". Maybe investing in various friendships which fill different roles is simply the way to go. That's not to say you must amass friends around you like some obsessive collection, but you have different friendships with different people. Nobody is going to complement you perfectly in all aspects of life and personality. By building a great foundation of close friendships, I am choosing which aspects of myself I most want to be brought out and supported.
And when I'm pining away for the "perfect friend", I sometimes think of ways in which I may be able to better extend my own love and friendship to those closest to me whose friendship has stood the test of time. Rather than waiting for the perfect friend (or romantic partner) to show up, I can work on perfecting the friendships and family relationships which matter most to me. What you value is clearly indicated by your investment. And sometimes you discover what you value by investing more proactively.