How to end it?

I’m stuck between a rock and a hard place. It’s coming up to 3 years that m s/o and I have been together but I keep having strong feelings of wanting new experiences and exploring new things; with other people. I don’t know how to end it with him, he’s my best friend and I value our friendship so much, I don’t want to lose him forever. I think a part of me too is just being selfish because I’m afraid that if I do end things with him, no one will ever love me like he does. I’m scared for that. But on the other hand too, I’m no being fair to myself because I’m withholding experiences from myself that would shape who I’m meant to be. I’m so lost