heart broken again

Back in February my wife, kids, Dad, and I went to Kansas for a funeral. While there my Dad promised he'd go camping with us on Memorial day. As usual he bailed on us. I haven't heard from him at all since February. You'd think after all these years I wouldn't let it hurt me anymore, but it still does. Even though I'm so angry and hurt, I still miss him and desperately want to have a relationship with him. I think what hurts the most is that I have no idea why he doesn't want a relationship with me.