And she tried in vain to force past her lips the words which she believed to be the truth, the words his pathetic, powerful face told her would end everything.

Yes, she knew he would not marry her if she told him the truth about her feelings.
"Do you mean that ?" he repeated, stern and sharp, yet sad, wistfully sad, too.
"I don't know what I mean," she cried, desperately afraid of him, afraid of the visions the idea of not marrying him conjured.

"I don't know what I mean," she repeated.

"You fill me with a kind of--of--horror.

You draw me into your grasp in spite of myself--like a whirlpool--and rouse all my instinct to try and save myself.