Open custody arrangement. Ex agreed to two months and refuses to give child back

You are going to need legal help. Right now, all you have are verbal promises.

Is your name on this child's birth certificate?

I have been through this. You need to see a lawyer right away. The lawyer will tell you what your options are.

My completely non-legal (but with some knowledge from how things work in my state... the law varies from state to state). You are going to want a restraining order from a judge. Then after that, you can file motions to get a parenting agreement. It is far better for your wife and you to work this out like reasonable adults... but it sounds like your wife has eliminated that as an option. If possible, be civil so that maybe you can work things out in the future (don't cuss her out, or call her names).

The most important thing.... Do not do anything further until you talk to a lawyer. You are in a custody battle... this is a battle. Anything you do on your own can and will be used against you. Basically, at some point in the not too distant future, you are going to have to stand before a judge and prove to him that you are acting more responsibly than your wife. The judge will judge you (that is their job)... and your wife will use any little thing you say or do against you.

So, my advice. Break off all contact with your wife, until you get a lawyer. If she calls you... tell her you are getting a lawyer and you will get back to her... say nothing else good or bad.

Then, don't do anything until you have talked to your lawyer. That is just the safest way forward when you are in a legal battle. And you are in a legal battle. Be smart, be responsible, be careful and yes... you have rights.

Me three on getting a lawyer.

This is why they exist.