Definitely take a break OP, but please don't think that everyone thinks you're lazy or that it's disgusting that your child isn't toilet trained yet. He's really not the only one. I work in a nursery and every year there are a good group of preschool children who haven't mastered it yet. Including by the time they leave us to go to school. 8 in a class of 30 this year.
They can't all have lazy, 'can't be bothered' parents can they? When you speak to these children's parents the vast majority are at the end of their tether with it all and feeling immense pressure to get it sorted. Many, like you, have tried all avenues and you have done everything that we would recommend - health visiting, ERIC etc.
It really does sound like he hasn't developed the signals he needs to have for this to work successfully doesn't it? And no amount of willing it to happen will make a difference. This doesn't necessarily mean he has additional needs and I'd like to think that his setting would have discussed any development concerns with you. The vast majority of children I've encountered with toileting difficulties don't have any obvious SEN at the time. Of course, we don't know what emerges later on. If you do suspect SEN there are a number of online sites that can offer toileting advice around this, though I suspect you've probably come across them.
In my experience most parents choose to keep going, but with the security net of a pull up - taking to the toilet at regular intervals and I would suggest that this is a good strategy to keep toilet awareness and confidence going. If he's happy to use the loo that is a huge step.
At nursery we then take children to use the potty/toilet at regular intervals plus when changing pull ups so it's part of their routine every day.
Pre school should be working with you on this and I really hope that they talk you out of removing him. Poo is part of the job, no one's favourite obviously, but an area of children's development that we need to account for.
Yes there are a section of people, including those working in childcare unfortunately, who like to cast judgement on toilet training. But it sounds like the person judging you hardest is you - please don't.