Sorry, I think it was over 4 years ago and I cannot remember exactly whether the security guard asked me to just show my ID card or he checked and then retained it. If their policy has always been to retain the joiner's ID card, he would probably retain mine. I cannot rememebr. In any case, it didn't and doesn't bother me at all. I seemed to remember that I was very welcomed to go up with my farang companion.
In your case, if your friend thought that he was having a romance with you he shouldn't have cared about this ID thing really. On the contrary, he would have given his ID card to the security guard as quickly as possible so that you both could have gone up to your room and been in each other's arms, kissing. I respect he probably had his own reason - - hope he did not carry too much formage on his shoulders !.
Anyway, if you bring someone to this hotel to find that he does not have an ID card with him your night and romance may be spoiled, and inevitably frustrating.