My understanding of "bad faith negotiations" is that if someone enters into a verbal or written agreement with you and walks away from the deal they are liable for any expenses you incurred.
I'm not sure where you gained this understanding, but it certainly isn't true. It happens all the time that persons and entities make verbal agreements and then back out during the process of memorializing the agreement in writing.
If he was just jerking me around do I not have good legal standing to recoup my legal fees?
Even if your understanding regarding "bad faith negotiations" were correct, how could you prove this. My reading of your original post is that your ex had little, if any, knowledge regarding your son's behavioral issues. Therefore, when he initially agreed to the custody change, he was ill-informed, and he changed his mind after spending time with the kid (the "frantic hysterical call"). I wouldn't put much stock in his comment that he "wasn't really going to go through with it anyway" (which he'd probably deny saying anyway).