Should I be worried?

My boyfriend and I have been together for 8 months now and we both just finished our 1st year of college and we stay an hour and a half away from each other for the summer, so  I went to go see him Thursday and Friday when I woke up I looked at his phone and there was an unknown number and when I opened his phone it was a girl and she was texting him and he called her beautiful, we talked about it and he said I shouldn't be worried and he said he was sorry and that he loves me and only me and he is never going to cheat. What should I do? I feel like I can't trust him now and even though he is telling me he loves me and doesn't want to lose me and that I am the one for him, I don't understand why he would text her that. Someone give me advice bc I'm super upset and having mixed emotions