Complex sentence: "Niki" (who was able to imitate Viki's mannerisms well enough to fool people into thinking she was really Viki) used Clint's transgression with Tina as grounds to divorce him.
Split into simpler sentences: Niki was able to imitate Viki's mannerisms well enough to fool people into thinking she was really Viki. She then used Clint's transgression with Tina as grounds to divorce him.