My girlfriend is not the same anymore.?

My girlfriend has been acting so different.like never happy. Yesterday morning she told me We need a break. Im sooo confused cause that night she came to my friends house where i was and telling be i better not cheat andsl stuff, but i dont cheat. She asked me if im talking to girls and stuff, and i dont. But meanwhile she text guys and then she left to go hangout with other people and wouldnt tell me who or where shes going. But she says she wants us toget better. Im stumped on whats going on anymore...