I need ADVICE please!

Now before you read these screenshots, I want to give you a little background info on my relationship. I've been with my SO for going on 4 years, and she helped me raise our son since he was 10 months old. We started dating when she was 14, and I was 15. When we first met, I cheated on her because I was still so young as I had no idea I would still be with her today. I didn't love her as much as I did now. She had so much passion for me, and she loved me beyond measures. Now...our love has died down. She doesn't love me as much and we argue all the time. She hits me sometimes, and it really hurts that she doesn't feel the same way that she use to. I really love her and I really want things to work. I'm so confused right now on what I should do...should I stay or should I go? ​​​