Ceremony Spell said:Wedding: You touch adult humanoids willing to be bonded together in marriage. For the next 7 days, each target gains a +2 bonus to AC while they are within 30 feet of each other. A creature can benefit from this rite again only if widowed.
True Polymorph is a high requirement, and regular Polymorph could only turn the insect into a beast.
Is it THAT hard to find a willing humanoid?
Divorce won't work. But I could see an evil aligned person or party being "serial widowers" as they move from town to town and marrying impressionable young people who never make it to the next town...

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.