If you found out that your daughter's or son's spouse was cheating on them, what would you do?

What would be your first reaction if you discovered that your son or daughter’s spouse was cheating on them? What would you say, and what would you do? Would you stay out of it or get involved?
The reason I am asking is that my husband is cheating on me now, three months after I delivered our son and had cervical cancer removed via an excruciating C-section. I have had serious postpartum depression as well.
To try to avoid arguing around the baby I asked my mother if the baby and I could come and stay with her for a few days and she said no. I asked her for asylum when I needed it the most and she denied me. I feel doubly betrayed and outraged.
If it were my child’s spouse there would be no place on earth that they could hide from me. I cannot describe the agony that I am enduring right now. It is slowly killing me.
Am I wrong in expecting my mother to at least show some type of solidarity with me?