Do I have the right?

My boyfriend of 3 years has a new female friend at his job that he talks to via text message and on occation over the phone.....Now this friendship makes me feel insecure and inadequate. I've expressed to him and he tells me that it's my problem and I have to deal with it on my own.....They're texting each other EVERYDAY for hours at a time, we a hugh fight yesterday and were discussing it via text message but he was texting her at the same time......do I have the right to ask him to stop or cut it down?