Complex sentence: Sue and Maud forge an unlikely friendship, which develops into a mutual physical passion; after a time, Sue realizes she has fallen in love with Maud, and begins to regret her involvement in Gentleman's plot.
Split into simpler sentences: Sue and Maud forge an unlikely friendship, which develops into a mutual physical attraction. After a time, Sue realizes she has fallen in love with Maud, and begins to regret her involvement in Gentleman's plot.