It sounds like you feel bad that you did not disclose your prior interactions with therapy with your new therapist so I believe to get the most benefits out of your sessions, it would be a weight off your chest to tell T when you are ready. Any good helper would appreciate this and not hold it against you. It is understanding that when first starting, the therapist is getting to know you as well as you getting to know them and have to establish a trusting bond. This information could be beneficial to what changes could be made to further help you if the prior techniques of your ex t did not fully help. Im sure your new T would appreciate your honesty and know you are serious about how much this means to you.