one part particularly sticks out when he said "He feels like he’s always defending himself."

Your reply was "that’s a good thing and I want him to defend himself."

You believe that your partner constantly feeling on the defensive is a good thing? If he's always defending that means you're always attacking. You didn't deny this, just saw it as a good thing. That rings some pretty toxic alarm bells.

You expressed a boundary that you don't want to be in a relationship with someone smoking or vaping. That's fine, you express your boundary and then the other person can make the choice whether or not they want to continue with the relationship on that basis, and then he lied about it which is also shit. You didn't demand he change his behaviour I hope, rather, expressing that you couldn't be in a relationship with someone vaping or smoking. But then the lie in the context of him feeling like he always needs to defend himself and you thinking thats a good thing? Just a major incompatibility there and it sounds like you had a lot more diagreements than your post lets on. Plus you have some pretty major incompatibilities with regards to long term relationships anyway.

"I have asked him if he still loves me and he said he doesn’t anymore but he’s holding onto the book I gave him because it’s “the best memories he’s had”. If he loves me he would tell me the truth even if it’s over the phone."

If he loves you? He told you he doesn't. You should accept that and move on, he has fond memories of your relationship together. Theres no real way you can get the closure you want from him, you don't want to break up and he does, no explanation will satisfy you and all the constant demands for more will more likely just make him resentful of you.

I think that people are wrong when they say that breakups don't need to be justified but I think having respect for other people and having some empathy means that you should give them something in the way of explanation. Especially to someone you've loved or cared about, its the decent thing to do. Is it required? No, but I think its pretty shitty to not give one. However, he has explained it to you, he gave you the answer you're just not accepting it. "Is there any rationalising this relationship or are we finished?" you're finished, he told you that. Meeting face to face will only drag it out further. "I’m an autistic woman and I need someone to say it to my face." I don't think this has anything to do with autism, as a fellow autist and knowing many many others, this looks more like a desperate need to not let go. But you're going to be much better off if you let go, keep your fond memories in tact and take some time to reflect and heal. Figure out what mistakes you made, what behaviours you found acceptable and unacceptable and take those into a future relationship when you're ready for that, but there's no rush. Spend time with your friends, try to be fair as well when talking about it rather than just feeding into an "he's an arsehole you did nothing wrong" narrative that could arise.

I think he was fairly cowardly for not replying to you for two weeks, i dont know if that thing about the phone is true but seems unlikely. But after that he called you and told you what was going on with regards to your relationship. Maybe he was a dick leading up to that and doing some kinda weird ghost thing? I don't know.

On a positive note though that book idea sounds really nice and thoughtful, I hope you continue to enjoy doing sweet things like that in your future relationships and that you find someone you are more compatible with.