So confused, please help!!

I’ve been with my boyfriend for almost two years. We’ve always been wonderful. He’s the nicest man and he really means a lot to me. But lately I’m finding that my feelings for him romantically aren’t as strong anymore. I keep finding myself posting cute pictures and wanting attention elsewhere. I would never cheat on him but I know it still isn’t fair to him. However I’m terrified to break up with him. I don’t feel as many romantic feelings anymore but he still means a lot to me. He really truly is my best friend and the thought of losing him is so scary. I don’t know what to do.