Olivia,
In our teens and especially in our 20s we grow tremendously. We mature. We find new interests. We discard others. Hopefully our self awareness grows. We discover new things, people, cultures. We uncover passions.
It is the typical “We’ve grown apart” talk. You want to find out things on your own without having someone holding you back even if he is not doing that explicitly.
Others here can better tell you the “How” to break up with him. Good for you for being clear on the “Why.”
I have been blindsided by my past relationships on breakups. You can feel terrible about not giving him signs but this also is typical in breakups. The person who breaks up usually has been thinking about it for a while before breaking up.
I got over my breakups. I looked to learn from those relationships. I am now in a fantastic relationship.
You are doing your boyfriend a favor by breaking up with him, the sooner, the better. It can be hard and even painful for you and him but in the long run, it is better.
Be directly honest. Be compassionate. Be brief. Do not be sucked into discussing or arguing on why you two should stay together. I find it hard when my soon-to-be-ex partner dances around the reasons, not being direct or honest when they broke up with him. In fact, with my last relationship, she was so indirect, I did not know that she was breaking up with me.
Mark