I dont think you will ever "get the old you back" simply because as we grow older situations and people change us and our character. As we grow older we develop into a "more newer style of person" If your bitter its because you are dealing with situations are make you bitter, it can be the product of a state of mind. Think about why you are bitter and use reason to changing this. Once you change your mentality and deal with what you need to deal with, you will be in a bigger, better place in terms of depression and anxiety.