They've been together for 20 years, and even unmarried, he still calls her his wife.

wife 是名词，指"妻子"，即已婚女性的配偶。虽然他们未正式结婚，但用 wife 这个词表示他们长期稳定的伴侣关系，暗示男方视她为终身伴侣。