I'm entering my final year of a BSc in Physics next year and have been looking for summer research opportunities, with the chance of possibly continuing my honours (undergraduate) thesis on the project afterwards. There was one particular professor I contacted since I took a course under him in the past and he seems like a great mentor. After looking into his research more, I was definitely intrigued and emailed him to speak about potential work I could do with him in the summer and later on my thesis (I mentioned in it if he would be okay supervising me for the summer/thesis). We ended up meeting and discussing projects (he gave me a list of possible projects), and although the work was still very interesting, I don't think the projects are necessarily lined up with my current interests and where I want to go. I'm still grateful for him being open to discuss potential work and meeting with me, and I certainly don't want to rub him the wrong way since he's honestly such a nice guy, but I also don't want to keep leading him on under the guise that I will be working with him in the future. At the moment, I am planning on just thanking him for all his time and for being very helpful, but that unfortunately after looking over the project, it seems like I might be looking for something different. Nonetheless, any advice you have on how to approach the professor about this (e.g. do's and dont's, anything additional I should say), would be greatly appreciated!