Complex sentence: He personally offered to hand over to Kavanaugh his personal notes outlining the evidence he uncovered linking the Strike Team with the heist but the relationship turned sour when Dutch learned that Kavanaugh's ex-wife, Sadie, had a history of mental illness.
Split into simpler sentences: He personally offered to hand over to Kavanaugh his personal notes, outlining the evidence he uncovered linking the Strike Team with the heist. However, the relationship soured when Dutch learned that Kavanaugh's ex-wife, Sadie, had a history of mental illness.