Im in two minds.

My boyfriend and I have been together for 1.7 years but I feel like things have changed ever since he's been speaking to this new girl constantly every single day. I wasn't against it at the beginning but now I seem to be so uncomfortable with it. They text everyday all the time, it's a 14 hour time difference. We are going through some issues but he does send me screenshots of their conversation. Now that's not the problem. The problem is that he hasn't told her he has a girlfriend and she talks to him like they're in the "talking stage" and he doesn't tell her anything. He sends me a screenshot of their conversation yesterday and in that conversation he asked her "missed me?" and she said "yeah I did" and then he goes on to tease her with this boy. He even tells her things like "suck my dick" and I find this really disrespectful. He even texts her before me. When we used to argue and he used to ignore me he'd be texting her. We're working on things but I feel like this relationship won't <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">nurture</a> until a third person which is her, is in the middle of it. This situation even tends to make me feel down most of the time. Am I wrong for thinking this and telling him to cut her off?