You need to look at what is best for YOU first. Do you want to be friends or do you not think you can be friends without getting hurt due to her not returning your feelings and wanting to make things right with her boyfriend?
If you want to be friends with her, tell her. She can't read your mind, you just need to say exactly how you feel: that you've drifted apart maybe and you wish to stay friends as you don't want to lose the bond you had with her.
If you don't think you can be friends with her without being hurt, you need to try and take some space. Yes, it will probably be difficult. Yes, you will miss her. But it will allow you to think things over and maybe even if you think it is best, begin to move on.
Nobody can tell you what to do though, or how to do it. You know your own mind. All you need to do is forget everyone else and focus on what is best for YOU.
I'm sorry you're in this situation, it's horrible having feelings for someone and not having them returned! But there will be someone one day that will return your feelings! I had this dilemma once with a friend of mine. She was my best friend and she moved schools (yes, I'm only 15) and I used to see her at least once or twice every week in the beginning, but then she got a boyfriend and I begun to see less and less of her. I knew before that, that I liked her, but this made it worse as I hated not seeing her as much anymore. She then begun to have relationship issues and I tried to be there for her, but it was very hard as I knew I had feelings for her and I didn't like her boyfriend and felt like she should leave him as he was treating her poorly, making her feel bad all the time and even controlling what she was posting on social media at one point! When I took a step back, however, their relationship ended as my friend decided it would be better if they parted and now its been a couple of weeks. I still haven't seen her though as she and I both have our mock exams this week and next week. The space has made me realise, though, that even if she doesn't like me back, I still want to be her friend as her friendship is something which I cherish. It may be different for you though. You just need to do what is best for you
And just remember, we can't help what we feel!
Hope this helped