Some people don't appreciate valuable things that come to them easily. You see it all the time when people devalue skills they possess that they have a natural knack for but wildly over-value things that they find difficult.
So it is with friends, sometimes.
The thing is, how does this affect you? I think it's having a bit of an impact on your self-esteem. You like her, are emotionally available and generous, and seem not to hierarchise your relationships. She isn't quite like this - and the fact that she is implicitly placing less value on you because you are emotionally generous is beginning to have an effect on your feelings of self-worth.
I think you need to put less energy into this friendship. Consciously start building other relationships.
Obviously, it's not worth falling out with her - it's not worth that. However, you're beginning to feel miserable. That is your emotions telling you that it's beginning to erode you a little. Listen to your emotions. Untangle yourself from her a bit.
You might want to think whether your emotions are telling you to stop being quite so emotionally giving, too. It might well be that all is fine - you just need to find people who appreciate this positive aspect of your personality for what it is, and who reciprocate in kind. Or it might be that you are changing and are entering a phase in your life where you want to be less giving, or to give more choosingly/sparingly.
It might be that, deep down, this is not a beneficial trait for you, or is no longer working for you. Maybe you feel that you are not a worthwhile person in your own right, and that people won't like you unless you are extra kind all the time. Or perhaps you have a habit of giving (at cost to you) that built up in your childhood. Perhaps you have just changed.
It might be any of these things, or it might be nothing at all. However, when something is making you miserable, it's always worth taking the time to really think about what is causing it, not ignore it, and to think about whether you feel like practising with new ways of living, interacting with people, etc. Change can be fun. We're not set in stone, and it does make life interesting.