Why is my urine split when I pee?

Anatomy. Physical changes of the urethra, the tube that passes urine from bladder to outside, could cause this. This may or may not be of importance. Your primary care physician should be very helpful in knowing that your kidney function is normal. A urologist otherwise is the right specialist for this.
Split stream. Occasional splitting of the urinary stream is common, especially in the morning. If this a consistent problem it may be related to a stricture in the urethra. See a urologist for further evaluation.