The jealousy between my co-wife and me keeps getting worse because our husband is clearly biased. What should we do?

Jealousy that stems from a husband's injustice must be dealt with at its root, which is justice, not merely by correcting the wives' feelings. The Prophet ﷺ said: “Whoever has two wives and inclines towards one of them, he will come on the Day of Resurrection with one side of his body leaning” (Sunan Abu Dawud 2133). A husband is obliged to be fair in the rota (turn of nights) and in outward maintenance (nafkah). Convey your feelings to your husband calmly and specifically about what is unfair, not by attacking your co-wife. If the injustice continues, officers at the religious affairs office or a sulh officer can help assess it. Meanwhile, tend to your heart through worship. See co-wife relations.