Complex sentence: Billy and Jill are close friends, and Billy subtly manipulates Guy and Jill's encounters and, after initially resisting Guy because she's returning to the UK, Jill falls in love with an equally smitten Guy.
Split into simpler sentences: Billy and Jill are close friends, and Billy subtly manipulates Guy and Jill's encounters. After initially resisting Guy because she's returning to the UK, Jill falls in love with an equally smitten Guy.