My question involves marriage law for the State of: New York

Actually this question involved my ex-fiancee - we never married. She is using a computer of mine on an email account I pay for. She gave me her password previously, and she has always had mine, I've just never looked at her emails (she has looked at mine). We broke up recently and I want to see what her true intentions about our child. Is it ok for me to read her email or install a spy text logging since it is my computer and email acct, or is that illegal?

thanks