your bf thought it was casual with this other woman and she didn't agree. that doesn't mean he lied. he may have lied, but it's quite possible she was hoping for more with him and convinced herself it was more. it happens all the time. the fact that he put on FB that he is in a relationship would lead me to give him a chance about it all because it appears he is being open and straightforward. i think you would do well to talk to him again about it all and tell him you read his texts. he probably won't be happy about that unless he's told you it is okay to read his texts.