I need help

Hello, I have been using this app for years now and I have never posted but I just really need some help right now. I have been with my boyfriend for almost 6 years now. We are young and we are high school sweethearts. I try to keep that in mind that we are so young and that can add to our problems, but I feel like by now we shouldn’t be going through what we are. We recently just got our own place together and I thought that would help but it’s not. I’m very insecure basically at all times. He makes me happy but I’m not sure it’s enough anymore. Because I’m insecure for what he has done in the past, I am constantly questioning him and do not trust him. I go through his phone and all that. But I find stuff I don’t like every time I do. We have only been living together for two months and I have been ready to leave twice now. It’s not healthy for me anymore the way things are going, but I truly believe he is my forever and he says the same for me. At this point, I know I can’t control his actions and he will do what he wants but I am here asking for advice for myself. I want to fix myself. I hate that I am insecure and overthink all of the time. I feel this brings more problems to the relationship then if I would just let it go. I just need advice on what I can do to help myself. I honestly don’t even care if he fixes himself anymore I just want to fix me so that I can be happy with or without him. Please help me.