Complex sentence: She falls madly in love with him on the spot, and he asks her to marry him (the same night that they met), which she promptly accepts, leading to a falling out with her former flame Frank Burns (Larry Linville).
Split into simpler sentences: She falls madly in love with him on the spot, and he asks her to marry him right away. Margaret promptly accepts, leading to a falling out with her former flame Frank Burns (Larry Linville).