Abuse and child custody

I've been divorced for 3 years and have sole custody of our 3-year-old. During our marriage, my ex physically and emotionally abused me on several occasions, but I kept the episodes a secret until after the divorce, when I told my family. I was also told by my ex's daughter from a previous marriage that he abused her and her mother several times. If my ex decides he wants custody (joint or otherwise) of our son, will the history of abuse keep this from happening? I have no proof. We live in Oregon.

proof

honey, you have the proof. his daughter. document things by date and times. get yourself a small pocket recorder tape conversations you have that give statements from others have them sup.into court, one thing that i learned from my attorney is that the tapes are admissable as long as one consenting voice is on tape which would be yours you do not have to let the other party know you are taping the conversation,per AZ state laws.