Flaky friend

I have a friend who for the past several months has been doing something's I don't appreciate and I have no idea how to bring it up to them. When we hang out they have made it a habit to make plans and they never get back to me. i just find it completely rude to make plans with someone and not even have the audacity to cancel or say, hey I don't want to do that anymore.

I think what's also frustrating is that I see them post things (on the days we are suppose to hang out) and they are doing things with other people. I have always been available and have been a support system to them. Am I over thinking it? I just would never do that to someone... how can I approach this?