Filing for custody in Virginia...?

My husband and I are seperating due to his infidelity. We had relocated to Virginia one week ago (before I found out) from Texas to be near my family. He now plans to return to Texas while I will be staying with family in Virgina. We have a 3 month old son. He has verbally agreed to grant me sole custody of our son. How do I go about doing this? Is there a custody form we can both sign and avoid a hearing?