Culture of today which is mainly from the western media makes people thing wrong about some acts which were been approved and even practiced by the Prophet (SAWA) and Ahlul Bayt (AS). If the western values calls your husband's second marriage with the condition of practical justice, a betrayal to you, then how do you look at a great lady like Ummul Banin (SA) who accepted many marriage of her husband Ameerul Mo'mineen (AS)?

Being unhappy with your husband's second marriage should not lead you to sinful acts like hurting him or accusing him or his second wife or her family or creating problems in the life of your husband even by changing your mode with him. You as a sincere believer in Allah, should accepts whatever Allah Has approved, and never show unhappiness with an act approved by Allah.

Your patience and acceptance to Allah's religion will give you a higher degree and great reward and will definitely make your life more successful.

Wassalam.