Should i be concerned ?

My boyfriend whom i've been with for a year and a half recently started texting this girl from his drama class. Turns out they text from the time they wake up till the time they go to sleep. He has never had a friend thats a girl in the time we have been together so yes it is different for me. When i say something to him about how i feel about their friendship, he runs and tells her. She and him both say they are just friends and in no way have anything brewing. I still feel like there is something going on, because why else would they be texting all day everyday. He even would text her when he is with me, and if he doesn't answer and she questions why he tells her I was distracting him. He has made the choice to stop talking to her all together. I don't know how i should feel or what i should do. Someone please give me some advise !