All my relationships are now loving and harmonious

Harmony isn't unison. Two voices on the identical note make a thinner sound than two on different notes that happen to fit.

Useful for the relationships that contain real disagreement: the sibling with opposite politics, the friend who made a choice you would never make. Harmony there does not require one of you to convert.

It comes from working out which conversations to have and which to let stand. Most peaceable long relationships are quietly full of subjects that were settled decades ago by being set down.