Boyfriend

Natalie
Someone help. My boyfriend and I have been together for 10 months and it's been an up and down relationship. 
Recently he has been talking to some woman in Darwin, all night, all day, if they aren't talking on the phone they are texting or playing the Xbox together. 
I have trust issues from a recent relationship, and I've asked him to stop talking to her, but he only did that for two days. Now it's non stop talking again. She always texts him, always calls him, and if he doesn't respond within 3 minutes of her first text. She will call over and over again, or text again and again. Keeping in mind he is 22 and she is 34, I don't understand why she is talking to someone that's in a pretty good relationship, and she knows that. 
I'm now starting to stress and am losing a lot of weight and not eating properly over this. Someone please help me get rid of this woman! 😰