Big, HUGE disagreement

A friend of my daughter has a kitten.  The friend  can't have pets where he's currently staying, so I agreed to give the kitten a home, temporarily. I love cats, and he's a really nice kitty. 

My DH is infuriated at my decision. He said if it's not gone by next weekend, he's going to kill it. We have 6 pets (3 dogs, 3 cats) of our own. It had been 8, but two died of old age recently. So it's not like we're anti-pet. But he wants to keep the diminishing pet population the way it is. He's said that once the cats are all gone, he doesn't want any more. 

We're not speaking at the moment because of it. He works a distance away, so he has a place he rents during the week, and is only here on weekends. 

Due to his new job and -existing condition BS with health insurance, he's been without his ADD meds for the past 4 months. EVERYTHING has been setting him off lately. I thought he had said goodbye during a phone call last week, so I hung up.  He called right back furious that I'd hung up on him. He said it "hurt his soul" that I hung up on him. I said repeatedly that it was a misunderstanding on my part and that I didn't hang up on him out of anger or anything. I simply thought we were done talking, and I needed to get back to work. 

He called last night after he got back to the second house and left me a voicemail. I don't remember the exact wording, but it was along the lines of saying I'd painted myself into a corner with this cat thing.  

If this is how he's acting with me, I'm wondering how he's acting at work. EVERYTHING that I or my daughter did made him mad this weekend.  She needed to replace her cell phone, but she needed him to be there in person with her so they knew we weren't trying to do some identity theft thing. We'd already tried doing it ourselves. I'm authorized to make changes, but the account's in his name and in this instance he needed to be there to authorize it. When she asked if they could go before he left to go back up north, he got angry and started listing off all the things he still needed to do. He said she was being demanding and he wasn't going to drop everything to go help 

I don't know if this is something I should stand my ground on and say the cat can stay or not. In the 5 years we've been together, this is very odd behavior on his part. He's normally very easy going, not one to fly off the handle, and if he does, he's calmed down within a few minutes. Being a pet lover, I don't want to kick it out; it would be totally against my nature to do that. 

I can't even try to reason with him. No matter what I say, how I say it, tone of voice, whatever, he sees and hears it as being hostile, to the point that I actually do start getting hostile. He says we're partners, and he wants me to support him in this. 

Finances are bad, but doing this one nice thing isn't taking anything away from us in that regard.  

I don't get it.