I'm thinking about letting my pet turtle escape
Why are you thinking of doing that?
I believe he will be happier living by himself.
It's not okay to neglect your pets.  Most pet turtles are not familiar with the local landscapes, and they probably will not survive on their own without you to care for them.
I just feel like I'm smothering him and he should be able to live naturally and free. I think he can take care of himself.
How will you feel if you find him dead in your yard? Don't you think you will feel worse than you do now? A pet turtle really hasn't learned how to live in a natural environment.