very secretive man?

i discovered that my husband is very secretive w his phone because he wants to do things that he shouldnt be doing in a relationship. he wasnt like this before, not until after our separation. its like hes living a double life, a life wout me, and one w me. and i feel like hes not committed to me at all. hed check out women on social media, youtube, porn, you name it. what should i do about this? i feel like hes already cheating on me. he does always bring up cheating whenever we argue or when he gets upset at me. and when he talks about cheating, he says it proudly, w a smile on his face.