It's a name card of that girl guider from the other girl team, she left it to yugeon in case he wants to leave cuz she knew he gets bad treatment. Heesu calls her pretending to be Yugeon and she said you finally decided to leave, so he thinks that yugeon talked with her asking for help for leaving, but the fact is she offered herself. Also heesu is a perb at core so he thinks yugeon also wants to leave bcs he liked that girl. If you remember a mission were ML team fought with another team led by a woman, well the card belongs to that woman's guide.
Ooh I remember about that girl now, thank you so much for the answers!
Can someone help? What's the yellow card/thing Heesu finds in Yugeon's drawer? What's the connection of that yellow card with the assumption "Yugeon will run away with girl"? What did Heesu show to Yugeon in his phone? (⊙…⊙ ) sorry if I missed these from prev chapters