How do I learn to let go?

Day by day, God is teaching me more and more about who I am. My tendencies...My insecurities...Who I am in Him... The newest self-realization I've had deals with relationships.

I can't let go of relationships.

Friends from High School...from my dorm floor...Church...conferences, etc. I can't do it. If I put time into a relationship, and work to develop it - it kills me to let it go, to see it fade. I even feel guilty from time to time when I see a "former" friend on campus and realize that I've failed to keep in touch with someone. I don't know if this is God laying certain people on my heart and not letting me give up on pursuing and praying for these people, or it is personal insecurities and wounds from my past effecting my life today. One thing I do know, I've lost a lot of relationships over the past few years, and there are still times I feel the pain creeping back into my chest.