I don't think you did anything wrong by driving by your Ts house. That said, I think you should know exactly why you want to tell them and what you hope to gain from it before making a decision. Because this did cross a boundary that extends outside the therapy session, I think this is an instance thay you should take your Ts feelings into consideration before saying anything. This has nothing to do with honesty or dishonesty, good or bad or right or wrong. You simply did something out of curiosity and, so long as you don't do it again, it's over. It's telling your T that would turn this into something more.