How to survive with a demanding 18 month old who cannot play independently and needs constant changing stimulation? He is wearing us down to nothing.

I know this sounds like I'm just complaining about a normal toddler, but it just seems a bit extreme at this point. My husband and I are luckily both at home at the moment so we can take shifts but even then we are running on empty. None of the (very healthy/active) grandparents are willing to take him for more than about an hour at a time and very occasionally because they can't keep up with him.My 18 month old son has to have CONSTANT interaction/stimulation, and also gets bored very very quickly with any activity. For example, reading a board book with him looks like some kind of race where he flips to a page, points to a couple of things and demand I say what they are then flips on as fast as possible. And if I stop him from turning in order to read the text he will get very upset. So if we come back from the library with 10 new books, we will have gone through them all in 5-10 minutes and then he will be bored shitless again. Being bored usually means whining and crying and trying to get us to play with him. This is the same with new toys from the toy library. He will flit from one thing to another (we have to be playing too of course) then be bored again.Going outside to the park or playground is about the only thing that will keep him happy for longer than a few minutes, so we try to take him out twice a day if we can manage it but its not really sustainable to do it every day (he is in constant motion at the park too trying to run onto the road or hurt himself in some way or other). He likes walks in the pram, but again, he gets bored of it after 10 minutes. Same in the backyard even though there's lawn to run on, chickens, a sandpit, toys, sprinklers to run through, etc. Same with any activity we cook up to entertain him.... music, dancing, playing hide & seek, helping with chores, drawing, baking, playing with toys.... its all great for up to 10 minutes then back to bored whining/crying again. He even gets bored of food he likes after a few mouthfuls and demands something else.He also has always had separation anxiety to the point where we still can't leave the room to pee without him crying and running after us, and banging on the bathroom door. We have on the rare occasion found him playing on his own for a minute or two but then he will suddenly realise we aren't with him and get upset.My question is - is this a developmental thing that we just have to get through? Or are we preventing him from developing independence by indulging his demands for constant attention? One of us is always interacting with him. I wonder if I was alone at home with him like most SAHMs and had no choice but to let him cry sometimes in order to cook/clean whether that would actually be better for him.He is a great adorable kid but we are really being ground down, and wondering what's going to happen when the next kid arrives soon. Neither of us are working right now so childcare is not an option, and we really don't want to park him in front of a TV/ipad for hours on end (which is of course the one thing that can hold his attention).Has anyone else been through this? via /r/Parenting http://ift.tt/2hgKLiT