I suggest you not file a return with him unless you see the entire return first, including the W-2. You are jointly and severally liable for what's on the return, and you are every bit as responsible as he is for the accuracy of the return. If he won't let you see everything that goes on the return, then don't agree to the joint filing, don't sign it, don't consent to any e-filing of it.
You can always find out what the refund was that was actually issued on a joint return--just contact the IRS and it will give you that information. So he cannot hide the real amount of the refund and short you on your share of it.