Scared to be single... help

So I’ve been in a relationship for 3 years now.. we actually just celebrated our 3 year by going on vacation this past weekend. I’m 20 and he’s 22. I love him very much and he’s become such a part of me but I feel like there’s a lot we both need to figure out about ourselves that would require us to be single... I have very few friends left, and the ones that I do have are all in serious relationships. How do I go about this? I’m scared to be lonely and sad all the time but I know it’s what’s best for us..