When things thaw, they're coming out of deep freeze and warming up. You can thaw a chicken, and a chilly friendship can thaw too.
Anything that thaws is warming up after a frigid or chilly period. The weather thaws when spring hits, especially after a bad winter. When you take food out of the freezer, it thaws. When you have an unpleasant relationship with someone, that can thaw too. A warm, friendly gesture from one person to another can be a sign that their cold relationship is thawing. When you think of thawing, think "Warming up."