I could really use some advice on this. I really miss him?

Sorry to hear about the end of your relationship. That's very hard. It sounds like you and your ex still have feelings for one another though, and atleast it didn't end really explosively. You are at a time in your life when you need to focus on you and your career. That is what he's doing. Focus on your goals, school and spending time on you, your family and friends. That's what is most important, although right now it probably feels like he is the most important thing to focus on. Best of luck to you, dear.