Why is the relationship between Hagar and Bram in The Stone Angel by Margaret Laurence tragic?

Hagar and Bram barely see eye to eye on many issues - primarily about their work and social life. Many scenes depict Bram and Hagar as nothing more than bedmates, and, even then, Hagar is reluctant to share with Bram. The few times that Hagar does miss Bram, she is alone, in bed, at night; Hagar never longs for Bram during the day.