You will need to acquire a seamless texture, or make one.
In photoshop, cut the left and bottom of your texture, say 10% or where the pattern repeats, and paste them on top of the right and top respectively, or vice versa, on separate layers. Then using masks, blend in the hard edges. With good blending, you can effectively create a seamless texture. The larger the texture, the more seamless it will appear.
Can you post an image comparison of your texture getting "cut in half"?
If your texture is already seamless, it might be an issue with your texture origin. Shifting this can be found under Documents => Creative Imaging => Align 3D Texture => Set Origin