My husband has been polygynous for a long time, but I still suddenly feel sad. Does this mean I have failed?

Sadness that comes now and then even after a long time is not a sign of failure, but a sign that you once loved something that has changed. Healing is not a straight line; an anniversary, a song or a certain place can bring the feeling back for a moment. This does not cancel the progress you have made. Allow yourself to feel it, then return to a calming routine. Notice whether the waves are becoming less frequent and lighter than before; that is a sign you are healing. Keep strengthening yourself with worship, support and a meaningful life. If the sadness settles back in and is heavy, talk to a counsellor. You have not failed; you are healing at your heart's own pace. See mental health.