In the pre-Hellenic period, their relationship was described as the one between husband and wife, and there seems to have been a tradition which actually described Artemis as the wife of Apollo.
ɪnðə pɹˈiːhɛlˈɛnɪk pˈiəɹɪəd, ðɛɹ ɹᵻlˈeɪʃənʃˌɪp wʌz dᵻskɹˈaɪbd æz ðə wˈʌn bᵻtwˌiːn hˈʌsbənd ænd wˈaɪf, ænd ðɛɹ sˈiːmz tə hɐvbɪn ɐ tɹɐdˈɪʃən wˌɪtʃ ˈæktʃuːəli dᵻskɹˈaɪbd ˈɑːɹɾɪmˌɪs æz ðə wˈaɪf ʌv ɐpˈɑːloʊ.