Apostasy

Recently, I've gotten back in touch with friends from late high school, early college years. Two of these friends, who were very strong Christians when we met have now become agnostic or athiest. This is a little scary to me. It bothers me that people can so casually toss aside something that is foundational to who I believed them to be. I'm trying to wrap my head around it a bit more, but don't think I'll really understand until I hear their whole story. I guess I just can't fathom not believing. I've been angry and hurt and confused and frustrated with God, but I always still believed He was there.