My girlfriend has started texting another guy?

My girlfriend of almost a year has started texting this other guy. I've never known her to texting him before but in the last 3 weeks she is texting him all the time while i'm with her. She hides her phone whilst she texts and deletes messages fairly regular so getting a quick look is often difficult. I dont even want to inspect her phone cause i want to be able to carry on trusting her as i do but this is really getting me down. When i ask who she is texting she says oh my friend and i've asked why she has just started texting all the time and she just says he texts me. They call each other up a few times a day and her phone rings alot while i'm with her and she walks in another room or just doesnt answer it. He lives 10 miles away and neither of them drive but the other day she opened her diary and out fell a train timetable for guess where? The place where he lives. She said she just picked it up cause she went for a walk in the bus station during her lunch break from work. Thanks for taking time to read.