Complex sentence: For the first years of the courtship, Keynes maintained an affair with a younger man, Sebastian Sprott, in tandem with Lopokova, but eventually chose Lopokova exclusively.
Split into simpler sentences: For the first years of the courtship, Keynes was actively bisexual. He maintained an affair with a younger man, Sebastian Sprott, in tandem with Lopokova, but eventually chose Lopokova exclusively.