H E L P

Okay before anyone starts.... don't wanna hear it! I have suspicions my husband is cheating on me. I need proof but I'm not sure how to go about it. He's denying it obviously. But he has an Ashley Madison account. He doesn't know I still have his iCloud information, so my question is, if I use his iCloud email under iMessage on my phone, where it says "send and receive" and then you go there and it says use your Apple ID for iMessage.... can I read his texts? Will he know I'm reading them? I need a little help. As soon as I get proof I'm leaving him. No married man has an Ashley Madison account for no reason! Right?! 😭 please help, thanks!