The others are right, but I'd just like to add something
You said "I love my boyfriend--I truly do"; "when I see him things are always so good and we just get along great"; I think that when the time comes to break up with him (not any time soon I hope) ...
So, if I understood well, you do love your boyfriend, you have no problems getting along and are fine as you are now, together, you don't wanna break up with him in the near future, still you want that at the same time.
I honestly think your post itself is quite confusing, so that must mean that *you* are confused.
I'd recommend you take some time to think about your life now, if you're happy with what you have, and then think about what it would be like if you broke up with your boyfriend and just stayed friends... would you be happier?
In my personal view, you are happy now (from what you've stated, that is) and you seem to have a good relationship. Again, from my point of view, you we start a relationship, we think of it to last -as long as it will-, but to last, not with a break up in the near future because we don't think it's common to date the same boy for 4 years, even if you're that young.
So, after thinking a lot about the whole thing by yourself, if you decide that you do want to be in the relationship, you can just talk to your boyfriend and tell him that you're willing to make it work for you both, but that you're both young and maybe thinking "we're gonna last forever", or "we're gonna date all through high school", while not bad thoughts, they might hurt you in the future, or create illusions in your head that will make you do the wrong mooves. Tell him you will be together for as long as you feel you're right together, and you shouldn't put limits on a relationship like a goal to reach, because it can, among other things, affect the way you two relate to one another and to the relationship itself - just like it's happening now with you, you're feeling unsure if a commited relationship is what you want.
I'd also like to mark down that a commited relationship is not the same as a "relationship forever" or something like that. It's just that you are commited and faithful to eachother for as long as you're in the relationship.
You are young, you have all the rights to feel you're not ready to be in a commited relationship with your boyfriend, maybe you just wanna be friends or have casual dates with different boys, so that's what you have to evaluate.
In the end, you're both young, and if you do decide to stay friends and are able to, it's a great thing, because you'll still be near a friend you love, and it's not impossible you two can hit it off in the future
I hope you get my point, I don't know if I'm being confusing with all this myself
So, think a lot, and good luck with whatever decision you make
P.S.: It's good that you don't want to be the cause of sadness to your boyfriend and that you don't want to hurt him, but it's not good to let that lead you to have a kind of life you don't want to for yourself. By talking to him, being open and honest with eachother, you won't hurt him as much as if you didn't communicate and just decided to break up. I'm sure if you do decide to break up and state why you want that, and that you're willing to remain friends, he will understand, and the pain he might feel will eventually go away with time and your precious friend's help Good luck!