7 month old crying when not in arms reach of Mum

[RetiredMom]

Hello Ladies.
I need some advice with regards to how to get a 7 month old, exclusively breastfed baby, to sleep in his cot, in his room. There are multiple issues, mainly my fault i guess, i am aware...
To give you an insight: since birth he has slept in the same bed as me, as he had reflux and colic for the first 4 months of his life and kept waking every hour through the night. He is exclusively brestfed and now, at 7 month wakes every 2 hours to feed, even yhough he has 3 solid meals a day and about breastfeeding on demand in between.
This wouldnt even be an issue...the problem is that he will not go to sleep unless i lay down next to him..and stays awake only if i lay there...he has gotten so used to me always being there that if i put him in his crib, or on a play mat after a few minutes he will become histerical, even when he can see me in the room. I tried letting him cry it out but he doesnt seem to stop ( yesterday he cries about an hour straight in his high chair while i was making food a couple of feet from him...) He is very intense and active...gets overexcited and overtired very quickly...Any suggestions on how to get him used to playing by himself for even an hour? I would just love to have a shower in the quiet...
Thank you all :)
An so very tired mum.