I need to vent my anger

So I'm watching my nephew. We go out to eat. My boyfriend gets him in the car. He's driving & I notice the car seat is not strapped in. I yell at him and he said it's fine, were only 5 min from home. I said I don't give a fuck, you wouldn't do that to your son. He kept saying it's not a big deal. I swear he does this stuff to piss me off. He's only 1 years old. Like anything can happen in 5 min.