How should a wife act upon learning that her husband is participating in horse betting, knowing that it is forbidden, and is lying to her about it?

If horse betting is a competition between horses for a prize, it is permissible under certain conditions. However, if it is merely predicting the winner among them in exchange for a prize for whoever’s prediction comes true, then it is forbidden gambling. You must strive to change this evil by confronting your husband and explaining the unlawfulness of his action and its consequences, or by clarifying the religious ruling and deterring him from this evil yourself or by seeking the help of others.