I think my girlfrend is cheating on me!??????????????/?

For the past few weeks ive been going out with my guy friends and she has been going out with her girls! But recently she has been weird, she ahs been really odd like as if she feels guilty and being quite quiet! I looked through her phone and she had messages from boys called charlie and sam calling her babe and hun! I mean why would other men be calling her that! Ive been checking her phone regualry since then and i continue to see texts about how much fun theyve had and how much more they plan to have!!! I mena even her emails are becoming full of things which she hasnt told me about like when parties are happening! Why am i not invited!! I know i go ou twith my boys but thats different i can be trusted and clearly she cant!