You need to look carefully at your Final Judgment and see if you were granted sole parental responsibility. In that case, I do not think that you would need his signature or consent in matters involving your child. However, what type of "legal" decision are you making that affects your child? I think that is the bigger question here.
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From what you have said in your comments in addition to your question the answer is most likely not because you have sole physical and sole legal custody, just doublecheck and take care.
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