My fiancé gave my chlamydia

Fiancé: 25

Me:19

went to the doctor several days ago because it was hurting to pee. It turns out I chlamydia. I haven't been with anyone besides my fiancé in a year. I told her my results and that she needed to get tested but was also wondering how I got chlamydia. She said she already knew she had it. She tested a while ago. She said she got in from accidentally putting on one of her friends dirty underwear a month ago. I didn't know you could get chlamydia that way. I asked why she didn't tell me and she said she was just embarrassed. I understand but I feel like I should have a right to be upset that she didn't tell me.