Well, you're a man now, so you're gonna have to start learning to be brave enough to speak about your emotions and thoughts.
A lot of dudes think showing emotions is a sign of weakness, and while that's sometimes true, it's also true that it takes way more bravery to express emotions than it does to hide them.
Talk to her, let her know how her behavior made you feel. If she still doesn't care after that then you gotta let her go. A relationship where you're the only one who cares is completely one sided and can't last.
This is all about love and respect, both for yourself and for her. If she's not willing to love or respect you, then for the sake of self-love and self-respect, you gotta get rid of the toxic element.