How to stop over thinking?

Ughhh! I need your help. I met a guy that’s great. I’ve written about him on here before. We spend time together and connect so well. We agreed to take things slow as he got out a four year relationship a year ago. He wants to really get to know me and I want to get to know him well too as it took me months to see my exes scary side. Things are moving fast between us but it’s not rushed as it’s all happening naturally. It’s crazy to think it’s only been a month. Last night we had “the talk” and we both know we really like each other but he can’t say what he wants out of his right now because he doesn’t know me well enough. I understand that. I know I want a relationship and marriage in general but I can’t honestly 100% say I want a relationship with him as it feels weird b/c it’s too fast to say that and I don’t want to be in a relationship that’s rushed. He treats me well and things are perfect but it’s still very early on. Sometimes I make myself sad over thinking maybe he will never change his mind or want to be with me or maybe he will decide he wants to date other ppl being that he was with someone for years. He does spend lots of time with me and use gas to come visit. We have made plenty of plans for the future as well. He really doesn’t have to give me his time and effort. He treats me so amazing and makes me feel so important unlike past relationships. How do I just relax my mind and take things day by day without worrying so much?