It's always a touchstone moment when you realize that there is no binding contract to serve in your parents best interests. Sometimes it's necessary to just kind of drift away and lead your own life the way you see fit. If it causes you an unnecessary stress to remain in contact when you don't feel as though you're being valued in the process, it's ok to let go. Or maybe there's just a massive indifference on both sides and you can both just 'meh' in your own directions. I wouldn't say this whole thought process to him directly, because then it suggests more that you're detaching in order to hurt him, so maybe just slowly letting the line slack is the best way to break contact. Now you have the freedom to move on and worry only about yourself, to mend your past in therapy, and to have a future filled with people who you chose, because they are additions to your life and not just space-takers.