Complex sentence: When Gillum was around 12 years old, his mother began dating a woman, Melissa Mills; this initially confused and embarrassed Gillum, who didn't understand the change in his mother's personal life.
Split into simpler sentences: When Gillum was around 12 years old, his mother began dating a woman named Melissa Mills. This initially confused and embarrassed Gillum, who could not comprehend the change in his mother's personal life.