If you are disillusioned with something, you are disappointed, because it is not as good as you had expected or thought. I've become very disillusioned with politics = disenchanted. disappointed because you have lost your belief that someone is good, or that an idea is right = disenchanted disillusioned by/with
Disillusion is the same as disillusionment. There is disillusion with established political parties. to make someone realize that something which they thought was true or good is not really true or good