Having Two Parents To Depend On

I have found that my ex husband no longer wants to help with the responsibilities of raising our daughter. He has left it all up to me. He doesn't want to hear about her grades, what classes she's taking and shows no interest in the up-coming birthday party we are having for her. I really don't think it's fair, but on the other hand, it's kind of nice not to have to argue with him over these issues. My question is this, though: Just because you divorce, does that mean that your partner no longer has to help in the raising of your children? I don't think so because I believe that once a parent, always a parent and he should be helping or at least interested in what's going on in her life. I have always felt that he should be able to call her at any time to hear her voice, see her when she wants to see him and allow him to participate in her school activities. However, this ex of mine has just acted like he has forgotten all those important steps in her life and growing up. Does anybody else have this sort of problem? What ever happened to having both parents for a child to depend on?