is he cheating

hi dads I need some advice. as men how to know if my spouse is cheating on me? he gets very sensitive when I want to see his phone bc I feel paranoid (he has cheated before emotionally before we were married) i gave him an ultimatum once me&baby or his phone and he chose his phone over us. I feel I know the red flags of cheating but idk what to do. am I really over thinking??? #pleasehelp #advicepls #youngparents