Complex sentence: Jane serves as a foil for Diana; though Diana loathes Jane's religious piety and ultra-optimistic outlook on life, she and Tom often help her when it comes to the matter of dealing with Harvey's manipulation of Jane's love for him.
Split into simpler sentences: Jane serves as a foil for Diana; though Diana loathes Jane's religious piety and optimistic outlook on life. Diana and Tom often help Jane when it comes to the matter of dealing with Harvey's manipulation of Jane's love for him.