It's unlikely custody will be taken from you if you've been the only one raising the child, however custody is determined on a case by case basis. You must honor the no contact order and should stop with the negative remarks, both for your legal sake and for your child's sake.
Disclaimer: This email message in no way creates an attorney client relationship between Majeski Law, LLC and the recipient. Responses are general in nature and do not constitute legal advice. You should consult a lawyer regarding any specific legal matter.
If you're a good mother and are taking care of your child, then the chances that you'll lose custody for making some upset facebook comments is unlikely. Even if he gets an order of protection against you, it's unlikely that you'll lose custody completely.
However, the things you post online may be used against you at some point in the future. I would suggest that you keep your angry comments to yourself or express them in a less public way, such as talking to friends or even a therapist. It's fine for you to be upset about having to raise a child on your own, just make sure you don't leave any ammunition behind that someone can use against you later.