馴れる
なれる to become domesticated to become tame to get too familiar with

馴れ初め
なれそめ start of a romance beginning of love

馴れ合い
なれあい collusion conspiracy illicit intercourse liaison

馴れ合う
なれあう to collude (with) to conspire (with) to establish a secret liaison (with) to make friends with to get along well with to become intimate (with opposite sex)

馴れ馴れしい
なれなれしい over-familiar