This is why I told you in my very first posts to you to GET LEGAL ADVICE. Your attorney can help give you the "best case/worst case" scenarios, so that you can make an informed decision about your risks, rights, vulnerabilities, etc. Have you talked to one yet??
No one's asking you to gamble away your visitation/custody with your kids ... you're getting WAY ahead of yourself. Wanna know what ONE THING you should do? You're right, don't spend the $$$ on a PI --- spend it on a bulldog, "men's rights" family law attorney, who specializes in father's rights and paternal custody issues. Get a consultation, and learn more about what you're dealing with here.
"What is best for my kids is best for me"
Persevere = happily being patient over a long period of time