Do you think he’s cheating?

My sister sent me these. Her husband (we’ll call him Adam) drove up to his dad’s (2 hours away) Saturday and spent the night there. His dad married his current wife about 2-3 years ago and has a daughter around 23 years old. I should reiterate that they’ve only been around for a couple years and Adam has only met them a limited amount of times, he doesn’t know them very well.

My sister looked through his phone the other night because he was acting weird (yes, she shouldn’t have, but it happened) and she found texts between Adam and his sister-in-law. She said it appeared that some texts had been deleted too because the beginning of the conversation seemed to be continued from a previous one. She also checked his Facebook messages knowing that he previously had a thread with this girl, and the whole fb thread had been deleted.

The texts sound very flirty and indicate that he went to this girl’s house Sunday morning before he drove back home. The last text he sent let this girl know that he made it home safe. My sister said she was out at a birthday party and didn’t make it home until late, Adam never told my sister that he got home, she didn’t know until she came home. They have 2 toddlers together and my sister is freaking out. I think he’s definitely cheating (maybe not physically but still cheating) but she doesn’t want to believe it. What do you think? Below is his text convo then fb messages of my sister talking to the girl.