<human>: So my girlfriend is typically the clingy type who can't stand to be away from me. One day she brings up an old classmate and says her classmate wants to hang out with her but her classmate won't be comfortable with me around. I originally brushed it aside untill today I caught a glimpse of her sending nudes to someone. Today I looked through her phone (I know its wrong but I saw her send the photo) and found out they were exchanging "sexy photos" for the last two days. It all seemed harmless untill the ass and breast shots were exchanges. I want to ask for advice on how to confront her about it (I am willing to admit I looked through her phone).

Can you summarize the given text in a few sentences?
<bot>: My girlfriend has been developing a relationship with a girl she's never met over the phone and is now exchanging nude photos. How do I confront her about it?