Between you and Yelan, there's always been some sort of a tension. Romantic or not, it's always been there. You, as an informant and her as the spy that uses the information you give. She organises an intel drop-off, flirts with you a little bit, flatters you until you give over the information in it's signature rose-tinted envelope with her name eloquently scribed into the front. With a wink and a whisper, she'd be gone at a moment's notice. Oh, how she twisted her words and yours was so infuriating yet so entrancing.
That night, as the storm that had been stalking Liyue for some hours now comes down over the harbour, and rain litters the markets and stalls alike, you browse for groceries to make dinner with. It won't make itself. As you pick up bits and pieces for food, a hand roughly grabs onto your collar and slams your face into the stall, immediately pulling it back up to stare at you. It's a Fatui agent, staring you dead in the eyes. "You feed the Qixing information." He snares to you, hand pulling tight on your collar.
That night is one that flicked through your mind as you handed Yelan the envelope at the next meeting. The envelope isn't rose-tinted nor has her name written on it. That same Fatui agent gave it to you, and you're sure that it has bad intel that will lead her to an ambush or worse. But, it was either you give Yelan the envelope and live, or don't give her the envelope and die. Self-preservation is only a natural human instinct, yet you can't help the guilt that aches as she still smiles and winks at you, headed for death or worse.
Your assumption was fully correct. The information in that letter had led her to an ambush, and a brutal one. The whole time she was fighting for her life, Yelan could only think about your betrayal, and how you'd sent her off to die. Mentally and physically exhausted, hurt and strained, she fought sloppily. Slashes and arrows fly, cuts and stabs hitting her and making blood drop. Yelan keeps going, determined to keep going.
And now, today. She brought herself home, patched her own wounds and got herself up and running again. Her hands still shake when she thinks about you, shaking in anger or heartbreak Yelan doesn't know. She hasn't seen or heard anything from you, for better or for worse unsure, but she also hasn't left her house since she got back. The rain still constantly pours, unbroken from when she left for that mission, and it's ruining the makeup she'd used to cover her cuts and scrapes.
Conveniently, as you sit down at the usual table you would exchange information at, Yelan walks into the Yangshang Teahouse, seeking some comfort in the tea's familiar taste. She sees you, and her heart picks up, first in anger and then betrayal. She sculks around your table, eventually sliding into her usual spot across from you silently. You don't even notice, staring down at another rose-tinted envelope, her name still scribed on it. "...surprised?" She chimes, coldly as you look up in surprise.