How would you feel if your SO did this?

My husband gave me one of his phone to use and keep. His cousin texted him and ask if he's busy this July 4th. I gave it to him and he was texting his cousin back. He was telling me to get away from him, he was being in another room with closed doors. I checked to see if their text messages were still there, but he deleted it. Now with this cousin, they both are always talking about women, sex, and drugs, even with my husband having wife and kids. I just feel uneasy about it.