I was thinking the same thing that zzzzz said - this is the third time you have discussed terminating in as many weeks - first it was because you didn't think you wanted to be pg, the second time because you thought there might be a slight chance that DC2 could have ASD, and now this. It sounds to me like you are seeking an excuse.
You need to discuss it, and WITH your DH - whether he has you pissed off or not. Just a bit of tough love here, but the DS you have with ASD - he is not just YOUR DS, but your DH's, too. Have you thought for a moment that DH is as stressed and upset about all of this as you are? Perhaps he is blaming himself for your DS's ASD (as you say he has AS himself, perhaps he thinks he is responsible for your son's challenges). You have asked him to do all the work that involves emphasizing DS's challenges and struggles, and nothing about his strengths... how can he not be beating himself up about this?
There have been a lot of wedges driven between you and DH in the last while - rows over you wanting to leave the UK, not wanting the pregnancy (you know, unless it was non consensual, intercourse without birth control occasionally leads to babies... you made a decision, conscious or not), expecting him to take total responsibility for all of the very emotionally taxing paperwork. Yesterday, the DLA form was put in his lap, and he got upset when you accused him of ignoring you. You can't have it both ways, and frankly, I see a lot of relationship sabotage here.
Scenario 1 - You terminate this pregnancy, knowing full well that your DH does not support this idea. In all likelihood, with how you are describing your relationship right now, this will end it. Are you ready to be a single parent?
Scenario 2 - You have a mature and respectful discussion with dh about where you are right now and how to move forward. You acknowledge why each of you is struggling (and you might be surprised what you learn through all this) and form specific and measurable goals together.
You have admitted here before that you struggle with mental health issues of your own - it is time for you to seek support personally (or increase support if you already have some in place) as the toll this is all taking on you is very obvious.
You keep saying how important your son is to you in all of this, but I worry that at least part of that is talk. If he was so important, you would not still be moaning about the lack of statement request submission after 2 and a half years, you would be making it happen.
Any of the regular posters here know I am about as subtle as a brick through a plate glass window, but sometimes it is necessary to stop fucking around and say it like it is.
No one is going to send out a rescue vessel to your unhappy boat of doom - if you want to get to shore, you need to handle the oars or get out and swim. You have a life vest, and the sharks aren't hungry, but it is going to take effort. That, or you can keep drifting, and that hasn't been working too well for you.
Quick tip - when you are bailing water, you are supposed to be pouring the water OUT of your boat, not into it.