19 and needing relationship help

I’m 19 turning 20 Nov 18th and I don’t know what to do anymore. I’ve been with my boyfriend for over 4 years and feel like I owe my future to him but another part of me wants to experience dating. I feel like I get in my head and tell myself what if I regret leaving him. What if I never find someone like him. But at the same time I know that I don’t love him like I used to. I love him in a way that I feel like I have to but I find myself wondering what if I dated this guy, or what if I had some fun with this other guy. I never would physically cheat but I feel like I am mentally even though I’m not actually talking to anyone or even friends with anyone I’m remotely interested in. I don’t know what to do.