Son and daughter in law separating

My son has told his wife of almost 15 year, with two young children (6 & 4) that he wants a separation and probably a divorce. He has already moved out. My daughter in law is devestated and my grandchildren are missing their father and can't understand why he has done this. I have tried speaking with my son. He has many reasons why he wants out of the marriage and really does not want to work at saving it. I don't know what else to do. Neither my son nor daughter in law have actively asked Christ into their lives but my daughter-in-law does believe in God and I believe is seeking Him at this time. I would really covet the prayers and insight of Christian women who have gone through this or who are compassionate towards those who are.