Afraid it's over after ten years together

Me and my SO have been together for ten years and now I'm really scared it might be over. We have two children, aged 3 and 4 months. I'm suspecting that our oldest might have autism and want to evaluate him for it. This is something I feel strongly about and he has known this since the day we met.

I have a baby sister with autism and my parents refused to see someone to get a diagnosis. I ended up calling my country's equivalent of cps on them because of this and they were eventually forced to do it. Sure enough she has autism, but because they fought it she didn't get a diagnosis until she was 13, which really fucked up school for her, because in our country you don't get any form of assistance or extra help without a diagnosis. She has now dropped out of high school and literally has no future, because you can't get a job here without a high school diploma and also she has never learned how to handle herself, as my parents just ignores her needs.

My SO was with me through all this. He sided with me. He knows I feel it's really important to get diagnosed as early as possible. But when I came home telling him how I think we need to do an evaluation on our son he started yelling at me about how he's perfect and that there's nothing wrong with him and how that's something we definitely wont do. Exactly like my parents acted with my sister and the exact reaction he condemned with me. I'm in total shock and this is an absolute deal breaker for me. I will always put my children's best first and I will do it whether or not he agrees (I can legally do it without his consent). I'm just so shocked by his reaction and absolutely heartbroken because I don't think he will come around and that will be the end of us. It's so unbelievable that a otherwise perfect relationship will end because of a thing like this. He refuses any counselling and it really hurts.

Edit: I don't want to leave him but he has said it's over if I do an evaluation on our son. The only reason I'm getting is because "our son is perfect and there's nothing wrong with him", which really rubs me the wrong way because it implies that people with diagnoses would be less worth and I'm having none of that.