Seatbelt issue

On Sunday, we were going to visit Lira. First and foremost, I want to say this: I'm grateful that JJ came. But, there was an incident on the way that really bothered me and dampened my mood. Merryn was having a little bit of a meltdown. She wanted to go to the bathroom but refused to put her shoes on; cried and whined the whole way to the restroom at the rest stop; wouldn't walk and wanted to be carried; and then she hit my face on the way back to the parking lot. When we got back in the car, I looked back at her after being back on the road for ten minutes, and saw she had taken off her seatbelt straps. I said, "JJ, would you pull over? Merryn took her straps off and I have told her that the car won't go if she isn't wearing her seatbelt." (This was an issue a few days earlier as well.) He said, "Merryn, put your seatbelt on," but he didn't do anything. I said, "could you please pull over so she takes it seriously?" He shouted at me, "I don't want to pull over on the highway!" I said, "well what should we do, then? We can't just let her ride without the straps on!" He refused to speak to me. I said, "JJ, why are you ignoring me? What should we do?" No response. "JJ, can we figure out a plan together? She has to have the seatbelt on--that's not negotiable." No answer. So then I climb to the back and buckle the straps. She undoes them again. I rebuckle them. She unbuckled them. Filled with frustration, I grabbed her hands and held them. I'm shaking with frustration. Several minutes later, I see that JJ is pulling into a rest stop. I say, "are you stopping here?" He says, "yes." We all get out and he's cuddling Merryn and talking to her. I didn't even want to be near him. I felt completely, totally undermined, disrespected, manipulated. He didn't say a single word to her about the seatbelt. I think he wanted to be the "good guy", in contrast to "crazy Mommy." As we were heading back to the car, I said, "everyone stop. Merryn, this was about your seatbelt. Daddy supports me on this. You have to wear it." Of course, he didn't support me. Even during that comment, he started walking away with Merrryn. And in the car, he gave her cookies. So, not sure what she learned there. She did keep them on after that, at least.