Problems with my EX wife and fiancee?

My EX Wife Stacy is pissed off that i am remarrying especially to my fiancee Dawn. Stacy told me i promised her i would never remarry and it will only **** up our daughter's childhood. Maybe i said that but i don't think it affect our daughter that much. Dawn told me Stacy isn't over me and is still in love with me. Stacy told me she isn't in love with me but we both agreed that were going to get remarried it would be together. I told her how that contradicted her earlier statement but she told me they were separate agreements. Dawn told me i am being a and i need to stand up to Stacy. Stacy told me she would take away my visitation rights if i marry Dawn. What should i do?