Should i be concern about it?

Ive been dating this girl for 6 mth now, and a couple mth she left her phone at my place and was getting phone calls and text every 5 min.. I think about until awhile that it kept on going, so i decided to check her text cuz i know some of her family members and friends.. But i saw something i didnt want to see.. A text from this guy that i thought was more then a friend.. then i saw a pic of my girl forwarded to him from awhile back that she still kept on her phone.. I asked her if is she was seeing anyone or going out with anyone and she said no.. So i decided to believe her, So a couple of mths i asked her to be my girl and she said yes..And weve been good a great relationship and everything, but she at my house right now in my bed sleeping.. And i just couldnt help myself to check her phone.. And yes there was another text from same guy.. Asking her ( baby are you home) What should i do?