<human>: My girlfriend and I have always had a lot of fun together, she is my best friend and the absolute love of my life. I planned to propose this Christmas, already have her fathers blessing. 

Recently I noticed her acting differently with our roommate, who is also one of my oldest friends. He's known for being a womanizer, always has different girls leaving in the same clothes they had the night before. I came home from work and they were quietly whispering in the kitchen, it sounded like a serious discussion, and when the door closed I swear I heard her say 'Shh! He's home' and when I walked into the room they shot apart. 

It could have been paranoia on my part I guess, but then last night when we were all sat watching some stupid reality show that she loves, she was on her phone the entire time. His phoned buzzed and I saw her name on his screen. They were texting while we were all in the same room. That can't be good can it? 

How do I bring this up? Do i confront her? Him? Do i need to sneak for evidence?

Summarize the given text in a few sentences.
<bot>: Girlfriend and roommate were texting while in the same room. Tried to deny it and hide it from me. I smell a rat.