Cheating?? What do I do!?

My husband is working out of town. I got a message from a girl sending me a screenshot that someone posted in the group are we dating the same guy -then my location. She asked if that was my husband. I immediately requested to join the group. The post said any tea or red flags? Then his name and area we are from and his Fb profile pic. I’m all over his profile so I’m assuming she wasn’t friends with him on Fb. The girl who sent it to me commented that he was married and tagged me. She immediately deleted it after she saw the comment. She also posted anonymously. I posted in that group asking for the girl to reach out to me.. she hasn’t. My husband swears up and down he’s not cheating. I can’t see any other reason for her posting unless they were talking. I’m about to end my marriage and we just had our second baby 2 months ago. What would you do if you were in my shoes?