Emotions also seem to act according to gravity. When in the presence of someone with whom you have a bond, and to whom you have entrusted your feelings, it is hard to lie and get away with it. The truth just wants to come flowing out. This is especially the case when you are trying to hide your sadness or vulnerability. It is much easier to conceal sadness from a stranger, or from someone you don't trust.
On learning that she had come from the future, the first thing he had wanted to know was whether ha had forgotten her, his wife. This realization filled her with both joy and sorrow.