I'm sorry this isn't helpful, if this is what he's like why did you marry him in the first place? Has he not always been paranoid and antisocial then? Sorry if I've missed something. If he is on the spectrum he would not have suddenly woke up one day like it, he would have always shown these traits. (disclaimer: not implying everyone with ASD is paranoid and antisocial of course!!)
There are a few possibilities here but nothing in your posts is enough to say this is a MH issue. That's not to say it isn't though. Also, it sounds as though his GP was for a referral for assessment for ASD, not for paranoid thoughts is that right? There is considerable comorbidity with ASD and psychosis actually, a lot of the patients I worked with in EI (early intervention in psychosis) had dx of ASD. However, getting a dx of ASD in adulthood is like hens teeth. Why does he want one so badly do you think? How would it affect his life to have a 'label'?
There is a delusional disorder called 'othello syndrome' or morbid jealousy. It centres on the strong delusional belief that a partner is cheating but with no discernible evidence to back this up. Apologies for the wiki link but it's actually quite decent and thorough.
en.wikipedia.org/wiki/Morbid_jealousy
However, you haven't said if he is even feeling jealous? If he believes so strongly you are having an affair, how does he feel about this? Is he hurt, angry, sad? It seems like all he's doing is ignoring you and threatening divorce. Where is the emotion here? Like I said, not enough to suggest a MH problem on its own.
Having said that, you really need to prioritise your safety here. If you genuinely suspect a delusional disorder then call your GP NOW and demand a psychiatric assessment. The MH team will call by the end of the day and speak to your H on the phone and then probably arrange a face to face assessment having triaged the situation.
If however, like others have said, this is just a selfish and cowardly man wanting out of his marriage for whatever reason then obviously there is no point wasting health professionals time with him, just let him go and start preparing yourself for a fight. Tbh I don't know why you'd want to remain with someone who you suspect will try to do everything he can to screw you over financially anyway. What a delight he sounds! 
Have just seen that you have an appt tomorrow, that's a good start. Hope you're ok anyway.