It is not up to the mother to forbid him contact with his son.
He needs to think of the long term ramifications of not being in his child's life and overcome any obstacles she may throw in his path.
Unless she can prove to family court that a relationship with the father would be detrimental to the son,she has no right to keep them separated.
He needs to petition the court for visitation.There is also mediation through family court and while it is voluntary,it is often helpful to have an objective third party help when the parents do not agree.