Does it get better?

Maybe you're looking for certainty, a certain answer for your son's future, so you will know what kind of steps to take, but it's hard for anyone to grant you that kind of knowledge. All you can do is take things one day at a time, one step at a time, and when he has to start school, just see where his development is at, and make your decision based on that. 

Also be careful about comparing him to anyone else, because he can only be himself. He might have sensory issues that overwhelm him and makes him have meltdowns or shutdowns, and he is in a strange world where people have already laid out all these expectations that are beyond his current level of understanding, so who knows the kind of pressure this little boy is going through. 

25 hours of ABA a week...no. Just no.

Perhaps instead of focusing on how to erase his behaviours, stop framing him as a burden and embrace and accept him for who he is. Then things might 'get better'. I am a happily married Autistic adult with a full-time job as a primary school teacher. Is that the kind of 'better' you want? Or do you want 'better' than that? If yes then it is possible, sure, but 'success' can look very different for different people. Maybe you should let go of your expectations. Autism isn't a disease or a terrible curse - it's just a different neurotype that needs a different response. Children often don't fulfil their parents' expectations, Autistic or not, but that doesn't mean they don't grow into fulfilled, adjusted people in their own ways. Of course as a parent you're going to worry for your other children, but your comment about your home being happy without him broke my heart. I'll be upfront and say I'm not a parent myself (what with my job I, of course, work with children, including Autistic ones, but I know my role isn't anything like being a parent) but my take on your situation is this: you have a healthy child, his brain just doesn't work in the same way as those of the majority. A little understanding and support in processing and regulating emotions - HEALTHY support, not support from some ABA 'practitioner' who claims that children can be 'cured' or made more neurotypical - goes a long way. Put yourself in your son's shoes...would you really want to go through 25 hours of hard, uncomfortable work a week, knowing that the full intent is to bend you into a more 'normal' person? Life will be overwhelming enough for him as it is; that's why he has 'tantrums'.

Edit: I'm sorry if this sounds blunt...I stand by everything I've said, but I am genuinely sorry you're going through a hard time. I'm going to respond emotively to this as it's an issue that deeply affects me. Many members of the Autistic community disagree with ABA and find it unethical. If you'd like to talk to someone completely non-judgemental and impartial, go to your GP (that is, if you're in the UK) - surgeries offer talking therapies that patients can be referred to quickly and easily. Maybe your getting some psychological help will help you manage the situation with your son.

Hi. My daughter is 3 and currently waiting for her assessment. 

I have days where I feel like that too. Tonight I had a cry to myself because my daughter likes to poo on the floor and rub it into the carpet even though shes complety clean through the day. 

We all have hard days we just have to ride them out. Is there anyone who could have him for over night  to give you some respite?? 

Have you spoken to his school.? SENCO?? see what support is out there for you at home??