Is it cool to be in a committed relationship with friends of the opposite 'hidden' from their partner?

I've been a relationship for two years. We have been open and honest up untill recently. She met this guy at her school that she think is so great, but will not let me meet him. Now she has this phone with his photo in it that she's always hiding. She tells me the phone is to keep time, but I've seen her talking on it, and I've seen the phone blink with tex alurts. Now I don't want to jump to any conclutions, but everything is very suspect. She tells me I'm just insecure. AM I?