I am one who loves deep conversation and to ponder on complicated questions.
Before I respond to your ex's behaviour, just to say, that who we are, as individuals, so shaped from mostly our childhood ie how our parents played things out. Mixed in, is our own personality that makes us an individual. We are molded by what occured in childhood and then, we, in effect, remold ourselves. NT's defintely have the unspoken ability to just get on with things. I encounter this often.
Your ex panicked. He imagined that telling you he is an aspie, caused him to freak out; expecting all kinds of horrors, which is actually a really good sign, because it means that you have touched his heart.
I have to say that for an NT, you are very eloquent with words! When one is faced with unknown situations, they have to compensate and you mention he was a particular aspie, who has no facial expressions, which means that in order to feel accepted, he mimics. I have done this in a very minor way; more to do with facial expressions and body movements. I actually felt I was that person.
What you need to do, is contact him and tell him that you are not put off by him revealing himself and want to be his friend. I think he falls back towards his ex, because she is his "comfort zone". He is too frightened to "stand alone", unless another woman comes along as can superimpose her goodness on to him, so in effect, swapping hosts!
My husband complains that he has emotions that need to be met by me, but what he fails to realise is that every single day, I have a flood of emotions, that I find hard to get a grip on, so actually, I need a strong man who can "carry" me through, and not demand that I give back. In other words: one has to be unselfish when in a relationship with an aspie, otherwise, they will feel: what about me and my emotions!