What helps me through the process of leaving my T is thinking that I am leaving HER (which is partially true-it's complicated). I know that sounds a little random, and possibly a little like breaking up with a significant other, but it's helpful.
So just think. You like your old T. But you've decided it's best to move on and find someone new who can help you and that you'll like even more. And you and old T can part on good terms and both move on as equals.
That's what I like to think anyways.