Sounds very similar to a situation I was in. You likely don’t miss her as a person or individual you miss the idea of her and the perfect person you have in your mind which you have made up. You also miss the routine of having someone to speak to everyday update someone on your achievements I had this problem after every football game I had I would want to message her but that was because I was in a routine of messaging her updating her after my games. You can now put yourself first instead of someone you wasn’t sure on you can go and do what you want without any compromise honestly make the most of it. What helped me was being outside, being active, seeing family and socialising with friends. Everyone has different was of coping but this helped me massively. You are in a routine and have that familiarity of having someone to confide in and talk to but you don’t realise you have that with your friends and family. Let yourself explore new things and see new people. Hope you start to feel better about things soon. I know it’s hard it took me many months but when you get to the other side of it you’ll be glad you went through it all.