I'm so confused. How do I address 'His fear (and the reason for crying) is that as soon as he relaxes, you will leave him and he doesn't feel secure enough to be left. So he stays awake until it's impossible for him to continue.' with being firm and stopping him pissing about for three hours?
There is no either/or in this. You can (and should) do both. Help him feel secure AND ALSO take no messing around. Indeed it is well documented that by being very firm with hard boundaries, that children feel secure just by having those boundaries.
Honestly I wouldn’t tolerate this from a 2.5 yr old, maybe I’m a monster but it would be a firm no to the climbing out and winging. I certainly wouldn’t have the screaming, that would a very firm telling off
This. exactly as PP said. Lets work this through...
So, your expectations should be:
(a) lie down in bed
(b) be still
(c) be quiet
Why? Because it will not be possible to go to sleep until he does all three. What you're not doing is insisting he sleeps. But you will/can insist that he lies down, is still and quiet. The idea is he then gets bored with no option to do anything else, relaxes and so sleeps.
How to do that? It's an unwelcome behaviour. You:
(1) Set clear, simple expectations
(2) No negotiation
(3) Respond quickly and firmly
(4) Be consistent
Develop your expectations into a mantra. For example "it's sleep time now. We lie down quietly to sleep. Nan night".
So, when putting into the cot, give him autonomy. Place him in standing up, tap mattress and tell him to lie down. Get him to go from standing to sitting to lying down independently without any help. Praise when he follows instructions. Play instruction following games in the daytime if you think might be an issue.
Once lying down - smiley face, compassionate tone, bend close to him and give him a "good boy" or whatever as praise. Hand on chest, repeat mantra.
Any movement toward getting up - Firm "No!". Immediately change your facial expression to stern. "No. It's sleep time now. We lie down quietly to sleep. Nan night". Tap mattress, tell him to lie down again, praise and change to positive/compassionate tone when instructions followed. Rinse and repeat. Over and over again - he needs to understand that the ONLY thing you will tolerate is him lying down.
If it's a big battle, make your expectations even simpler - forget being quiet (for now) but absolutely don't tolerate anything other than lying down. You have to be firm, repetitive and keep on going. You have to set those very firm boundaries so he understands that no other option is available at all, for the sake of his own wellbeing and because you are the parent and so sometimes he has no option but to do as he is told.
The messing around you are facing is a behaviour issue, not a sleep issue. You need to treat it as such.