Confused

I’ve been in a relationship with this guy for 2 years and 3 months. Things weren’t always great, we met when I was 16 and he was 17, and he was very immature. He did a lot of bad stuff to me like flirted with girls and just disrespected me. We did break up, and we got back together and he changed everything. He is very sweet and he always has been, he’s hard working, he’s caring, and he’s funny. He’s my best friend really. Sometimes I feel like it’s too late tho. We’ve been together now after our break up for maybe a year, where things are fine I mean at first it was a bit rocky because I was insecure. Sometimes I don’t know if it will work out. I’ve done the impossible for him I always have gone out of my way for him. I mean we are both so young. Recently I’ve tried to cut things off and he told me no that we were going to work things out that he was going to change things and be better for me and that he wants to someday marry me. We had got into this fight and I just always feel like he is hiding something. He never is actually doing anything where it’s cheating or even talking to other girls. It’s like where he talks to his cousins and how he tries to be sneaky. I feel like I’ll never be the only girl he has his eyes on. With everything I’ve been through I feel like he needs to be more sensitive with what he does or says. I guess I’m here trying to figure out what to do. I love him, I’ve always been all over him and crazy about him, but I don’t know why things are suddenly changing for me.