I don't like saying this, but it sounds like he still has feelings for her. I have been in a similar situation, where my boyfriend would go to his ex for advice all the time, and talk about our relationship to her, accidentally called me her name. He eventually admitted he still loved her. The fact that you are feeling the need to snoop in his private messages, and then finding red flag worthy messages speaks volumes. I can see this going downhill I really think you both need to talk about this situation. Sending hugs your way~