Before you screw up with a pro se case, you NEED a lawyer. Do NOT file pro se!
Since you have not legitimated the child, the mother had sole custody and you had to return the child (and could have been criminally charged). You should have hired counsel in May and not delayed.
A rule nisi is simply a scheduling of a court date. That may or may not be appropriate in your case, as different courts set court dates differently, but I suspect what your lawyer will actually do is to file for legitimization and custody and seek an emergency order or emergency temporary hearing.
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You are on VERY shaky ground. Since you have never legitimated your son, you have no legal standing to keep the child. You need to file a legitimation and custody action immediately and you need to request an emergency hearing. Filing a Rule Nisi is merely requesting the court to set a hearing date. Although you are legally entitled to represent yourself in such an action, the court is unlikely to seriously consider the case without a lawyer being involved. There are some things you can do for yourself. Custody is not one of them. I highly recommend that you contact counsel to assist you.
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