I really feel like I've fucked up and need some help knowing what to do to sort this out.
5 year old DS is football mad (fine). He completed a sticker chart for good behaviour a while ago and got to choose a magazine, except he actually wanted a pack of Match attax cards instead. I didn't see an issue with this as some other boys at school had given him so cards and they seemed quite good from a maths basis, so I got them.
The next time he completed his chart he got the folder to store them.
He loves them so much and I did notice they were starting to become a bit of a pain sometimes eg in the morning before leaving he would have to sort them into a specific order and sometimes this would make leaving the house tricky. I tried to set boundaries over putting them away at certain times but I feel like an idiot for not seeing the warning signs.
I don't usually buy expensive advent calendars for the kids, but I saw a really gorgeous one for my older DD (a bracelet with a charm each day). I really wanted to treat her as she's been so good with her schoolwork, music practice etc recently, so to even it up I decided to get DS a special calendar too.
I saw a match attax one and there wasn't even a lot thought, just that he'd love it so I'd get it.
I think this has been a big mistake. His behaviour over the cards has been deteriorating. In the run up to Saturday I considered taking the calendar back but stupidly decided to try and use it as positive reinforcement, and set boundaries eg open calendar after school and after activities so it doesn't get in the way.
He's had a really challenging few days and refused to do his activities at the weekend, is obsessing over the cards and getting the packet from his calendar. I had to remove all his cards and the folder all day Sunday after really challenging behaviour (refusing to listen, pushing, shouting- I explained clearly why) and gave a clear time he could have the back (today after swimming). Sunday afternoon without the cards was a transformation, we played other games and spent time together and he told me what a lovely time he'd had.
This evening he refused to do his swimming lesson and sat at the edge of the pool messing about. As we'd had a deal about him getting them back if he did his lesson, I explained he could t get them back today, but he could open his advent calendar (as I felt too extreme to not allow that considering DD is opening hers). He was upset about not getting the rest of the cards back, but seemed to understand. We agreed that when he gets 3 reward stickers he can have them all back.
However he's been really unsettled and whimpering loads tonight. He started full on crying in his sleep just now so I went in to comfort him as assumed bad dream. When I shushed him he said 'I just can't stop thinking about my cards taken away'
What do I do? This seems so obsessive and worries me, but because of the bloody advent calendar I've put myself in a bind. It seems so cruel to remove it but now I'm worried it's perpetuating the obsession and the issues were having with the cards.
I know this is my fault but any advice on what to do would be appreciated.
Should we remove them all and go cold turkey, replacing the calendar with something else? Feels very cruel 
But allowing him to have the cards - it's literally all he will talk about, all he wants to do, and leads to really difficult behaviour and problems listening, or leaving the house for school
And now I'm awake at 2am stressing, help! 😩