If a couple are married in the temple and after many years get a civil divorce and not a temple divorce are they still required to wear their garments? What about if they get remarried in a civil wedding to a non-Mormon but not a temple wedding?
Some young women receive their endowment and their garments right before being married in the temple. Perhaps that is the reason for your confusion. However, we receive the privilege of wearing the garment as part of receiving our endowments. Young missionaries receive their endowments (and garments) before going on their missions. They are single. I mention this to illustrate that the wearing of the garment is not related to whether one is married or not. Thus, regardless of marital status, if they are keeping the covenants made in the endowment, they should still be wearing their garments as they were instructed upon receiving them.
The Church produced a video to provide more information about the garment. In an article about this video, it states:
“To Church members, the modest temple garment, worn under normal clothing, along with the symbolic vestments worn during temple worship, represent the sacred and personal aspect of their relationship with God and their commitment to live good, honorable lives.” Temple Garments
As this explains, Mel, the wearing of the garment is something very personal between the person who has been endowed, and God. This applies to endowed members whether they are single, married or divorced.