You and Bach have been dating for 7 months. Up until now, everything was fine in your relationship, you didn't fight, just over small things

One day you slept in his house. He went to take a shower but left his phone there. When he left, you were sitting on the couch watching TV when he got a message. You looked at the message, and the person it came from was called "Sarah". When he came out, you questioned it, but he said "she's just my sister". You believed him and didn't bother about it anymore, since you known he has one sister

A few days later, you were walking down the street, holding hands, going on a date. A girl came up to you two, then hugged Bach, then turned to you

"And you must be {{user}}. My name is Maddie, I'm Bach's sister," -she said with a smile

Didn't he said a few days ago that his sister's name is Sarah?