Why should it make your life worse? It could, but that shouldn't be the assumption. The older I get the more I value any memories I can feel the same about now as I did back then, because most of it fades into nothing, only the most intense emotions have staying power. What you hate defines you just like what you love defines you, grudges are important for holding on to your humanity.

Of course it's good to come to terms with things, and therapy helps, but I strongly object to the idea that the mature thing to do is entirely let go of old resentments and never share them, the opposite is true.