Im a 18 m and my gf is 19f been dating for 11 months and i found out something…

Hello, i need some advice from someone mature and experienced because this is my first relationship and first body. She told me she had three before me 1 in a relationship. I am not a very sexual person and not really a person motivated by dating that much at all. But my gf and i have been friends for a year and fell for her to the point where i wanted to experience these things with her. I would be hesitant to talk about her past directly with her because it makes me uncomfortable, but i of course new things prematurely due to our friendship. However her and I have been having troubles where she isn’t giving the amount of attention and effort that she used too. I have tried to communicate this to her but im often left with “I dont know whats wrong” or “why is it never enough.” I usually respect what she says and recognize that she can be going through a hard time and i dont want to make it worse so i usually drop it. However out of insecure curiosity i went through her phone and saw how she treated past relationships before me. Completely different, more lustful, clingy and obsessive. She would regularly talk about hooking up and i have found out that even she had made out and wanted to hook up with her childhood best friend from her home country a few months before we started dating. The reason this concerns me is because she never mentioned this to me and even went back to her home country and stayed with him and a group of friends for a long period of time. Im going to be completely honest i know this girl very well and i dont see her cheating as a possibility hence she has suffered terribly from it. However figuring this out doesn’t sit right with me and i know i not only lack relationship experience but maturity as well. I find it kind of drawing me away from the idea of her as well as the fact we have had very strange boundary breaking incidents before but were never really a big of enough deal for me to change opinions. Any advice?