My ex left me and our son and know she wants to go for full custody what can I do to win the case:mad:

Tell the court that you don't want custody to change and tell them why.

Hire a lawyer. That will definitely help.

She will most likely be awarded some visitation. Almost no way around it. But courts are very hesitant to change custody if both parties do not agree on it. The general rule of thumb is "if it aint broke, dont fix it".