Would you believe the sister without proof

Over a month ago I made a post about finding out that my husband who I had been with since high school cheated on me. He didn't remember cheating on me. He went out with his on again off again best friend who doesn't like me. Hasn't been a good friend to my husband. Has stolen from us. He's a shit person. They went out drunk and he woke up with no clothes on and his friend said he fucked a girl. My husband told me and said he didn't remember but he's sorry and was crying. He's been sleeping on the couch over a month while I try to gain trust back. Our relationship hasn't been the same. Well his best friends sister texted me and said that his best friend told her that he was happy he ruined our marriage by convincing him to cheat and when she asked Joe he convinced my husband to cheat what she said he said was "By slipping something fun in his drink when he went to piss." She claims he admitted this to her but has no proof her brother admitted it. Would you believe her without proof... I've known my husband over a decade and he's never been the type to cheat but she has no proof