Hi Eandz. This is a story of hope for you.
My DS2 was officially DX at 3.7 (paed brought up ASD at 3.1) and only that late because my first DS had significant but NT speech delay so I just thought 'here we go again!' and didn't worry enough. (Oh, the guilt.) TBH to get a DX this young my DS had some classic and obvious symptoms. There was no doubting the DX for my DS, and he still is obviously autistic at 11. But, I have to say there are lots of advantages to 'not being borderline.' Getting support is easier, getting past denial and on to action is easier, progress can be more significant.
My DS2 is HF ASD but non verbal until he was 4. He comes on in leaps and then plateaus for ages (frustrating.) I have no qualms telling people about his DX, he doesn't care and it's bloody obvious there's something. He is pretty much happy, except when cross, but then he's cross and upset rather than sad and anxious and he gets over it quickly these days.
He got a place at a special early years school at 3.3 where I met great friends among parents and staff. Using PECs and Hanen "More than Words" he started to communicate. He talked in sentances by 4.5. By 5 he started MS school part time and could read, by 6 he was FT and had a statement. Now he's 11 and popular; despite not wanting any friends, the class like him. He plays alone but has just been voted school council rep by his class unanimously for the 3rd time. He's left today for his Y6 residential (wibble) and is going to MS secondary in Sept. He's age appropriate in literacy and above average in maths.
EandZ, there is lots of hope, lots of fun, lots of heartache, lots of battles. I love him to bits, and I truly wouldn't change him.
((((hugs)))) on your DS's DX. Take time to get used to it, allow yourself to grieve, because it's a very real grief. But you haven't lost him, he's just the same lovely and infuriating boy he's always been. You now have more tools to help him and more ammunition to fight for him.