Solstice — Joyce Carol Oates

Two women meet. One, Monica Jensen, is in her late twenties, vulnerable and insecure, not yet over the shock of her recent divorce, a teacher at a boys' private school in rural Pennsylvania. The other, Sheila Trask, is in her mid-thirties, the widow of a world-famed sculptor and herself a painter of stature, dominating, fascinating, restless in her need for what or for whom she seems unable to define, even to herself.
These two women meet. Drawn to each other, they become friends. Imperceptibly, hardly aware of what is happening to them at the deepest level of feeling, the move, or are moved, toward love, and ultimately beyond it, arriving at last at a near-fatal obsession with each other.