Insecure boyfriend

My boyfriend is insecure and every girl before me has cheated on him yet he acts friendly with his ex and after he told me he doesn’t talk to her anymore I see her snap name pop up on his phone and one time he left his Facebook logged into my phone and they had one of those secret conversations that deletes messages after a certain period of time. I don’t understand 😞 it’s like I’m not good enough for him but yet he’s scared Im gonna move on. Who knows who else he’s talking to behind my back