I think it sounds like he’s really tried to get on board because he wants to be with you (buying them beds, allowing them in his house, talking about a conservatory for them) but has realised it’s too much.
You said they’re better behaved now having been trained - were they quite yappy or naughty previously?
I had always been ambivalent toward most dogs - didn’t like most ‘doggy’ traits i.e. barking, being jumped on, but never hugely bothered me. It was only after moving in with an ex who had a small, smelly, untrained & yappy dog that I came to realise it’s tantamount to sensory torture for someone who doesn’t adore them. There were other more serious issues, but even if we’d been happy, the relationship would have ended due to my inability to live with a dog. It’s something I learnt while I was in that relationship, and I’ve been upfront about it to future partners - hasn’t been an issue since. Love having pets, but sticking with cats.
I think it’s hard to understand why if you’re a dog person, and it isn’t personal OP. Even if your animals are well behaved, quiet, etc. it’s the very nature of dogs that people seem to have to plan a lot of their lives around them and take them everywhere. That’s a huge burden and quite problematic for someone who is used to more independence or doesn’t love them to bits.
Unless you can accept his suggestion, and never have dogs again after yours aren’t here, I agree with others that you may need to reconsider this relationship. Your dogs may also pick up on not being wanted in their home.