I don't know what to do ...

So Me and The Girl(I'm also a girl) I'm With Was Together for 7 Months . I'm 15 , she's 17 and I've gave her chance after chance . The other day I was fed up with her flirting with someone else .. I went through her messages ! I feel like she's not mentally ready for a relationship and I used to juggle with girls , but I was faithful to her and this is how I got paid ! I guess it's called karma from all the girls I hurt ! But anyways I'm mentally older than her , but not physically . She acts like a little ass kid and also I bought her stuff for Christmas and her birthday and I really don't ask for anything , but when I do .. I get a sorry ass excuse , but she'd pay for stuff she doesn't need . I'm really not materialistic so I pay no mind , but I feel like I'm giving more effort than her ..tonight I Facetimed her and she put me on pause so I hung up .. I was kinda hoping she would call back , but she didn't .  Am I overreacting or ..? Should I talk to her ?