Mystery text at night.. I need your help ladies

Last night my husband and I were watching a movie on his phone and a Facebook message pops up on the top of the screen that read “are you awake?” And then another, 2 seconds later that read “I can’t sleep”. I asked him who it was and he said it was one of the investors from his investors club who he’s supposedly in business with. I automatically became suspicious because it was 3am and those texts were not about business. About 5 minutes later and attachment came through and he swiped it up and was made a comment like “omg this investor lady needs to leave me alone” or something like that. So I waited until the movie was over and he was asleep or I think fake sleeping and I took his phone to the bathroom. He jumped up so fast and asked what I was doing with his phone I was like on nothing I just can’t sleep and my phone is dying. His phone was still connected to the Bluetooth so he heard me unlocking it and stuff and he came to the bathroom like “don’t open the Facebook message because then I’ll have to respond and it’s too late”. Anyway long story short, I checked the messages anyway and there were no previous messages. The previous conversations been deleted. He’s hiding something I just don’t know what. Feel free to let me know what you guys think