suspicious about bf and his babymomma

Liz
My boyfriend talks to his babymomma when he can cause he wants to see his daughter. But, it gives me a very bad feeling in my gut because she's super manipulative and holds that little girl over his head like she's a trophy. On Friday (December 9th) I found messages between them that were fishy and caused me to break the phone the messages were found on. One message was saying that if he stayed living at his moms and got back together with her cause "she's 100% better then me" because she has a job that he could see his daughter. He left his moms cause he wants me in his life forever as his wife one day. It really thows me off with the messages between them. My solution is checking his facebook messenger since that's now the only way he can contact her. Since having found the messages I also realized she's causing all of my suspicion cause she keeps asking where he's at and that she's in his area. He's being vague towards her about things like that. I'm still suspicious and want to take screen shots of the real fishy messages when they pop up. Is that ok as a girlfriend to do if she wants evidence and she's suspicious?