He gets calcium every day, d3 every 2 weeks an he was also next to a window all summer. So basically he's gonna die from MBD eventually? is he advanced or can I save him or?
If that window was not open, then he got no beneficial uvb from the sun. uvb rays do not pass through glass or plastic.
We are not saying he is going to die.
His case is not the worst we have seen.
While the damage done cannot be reversed (ie his legs wont straighten out) the disease can be stopped.
You need to go toa vet who is knowledgable in chams, have them take xrays to confirm MBD, then they should send you home with calcium injections.
Until you can get him to the vet, outside time int he sun as much as possible, and go get some calci worms. (also known as pheonix worms) can be bought at petco.
I would try to get some hornworms too, which are great for hydration and I know that is an issue here too (orange urate= not enough water).
he can live a long relatively normal life if the right steps are taken now, before it becomes so advanced he is in alot of pain and has no decent quality of life.