How do you get over the loneliness and depression ociated with divorce?

Been divorced for a while now, have a civilized relationship with my ex wife, have been seeing her on a limited basis for coffee and conversation and am raising two children with her as well. Even though we text each other, use the IM to communicate and I see her in person, why do I feel so empty, why was I diagnosed with depression and why do I feel like life is not worth living even though I have a platonic friend to share activities with and am in excellent terms with my ex? Everything is going well with my life right now but my emotions are just going out of control even if I'm happy? Anyone else going through this situation?