It's been so long since I last played the demo LOL but iirc when you go to the spring festival, you can choose to split up instead of staying one group and from there, you and Cam can spend time w just one of the LI's at a time. If you spend time w Jamie, there's one scene where the 3 of you get temporary tattoos and you have to select the option where you get to choose the spot on your bodies where the tattoos are gonna go. There's normally like 3 options but if you have enough points w Jamie, a new one shows up. I'm gonna hide what the choice is in case you wanna find out for yourself, but if you wanna know immediately, click the spoiler.
Spoiler!
You can choose to get tramp stamps lmaoo there’s also a funny after-event text convo where Percy and Elio are flabbergasted that you convinced Jamie to get one