Cheating husband

My friend needs help. She caught her husband talking to a woman nonstop through phone records and she hasn’t confronted him yet. They were on vacay last week and she woke up at 2am and he was nowhere to be found, and the door was left cracked open so she went to the beach looking for him and found him down there on the phone. She looked at phone records and he talked to her that night for 223 minutes and other phone records say they talk night and day and have been for months. This is the 3rd time he’s cheated, and she’s scared Bc he’s abusive. They have 4 kids. How can she prove he’s cheating? Any ideas or advice for her? (I didn’t mean prove to him he’s cheating.) (HOW DOES SHE PROVE IT IN COURT)