Over the years I have come to care about and love my online friends just as I do my real life friends.
Online friends are basically always there - anytime you want to tell them something, share something, you pop them an email and it's already "shared" -- even if they don't respond straight away, there is some satisfaction in that.
You can also in some ways share things on a deeper level because they're not part of your "real life" circle, so it becomes less threatening in many ways.
My best female friend is someone I met online a good few years back. We're now real life friends too, but still write and share a lot by email. There is something cathartic in sharing through writing.