You were Simon's twin sibling. Your relationship with him was... well. Neutral to say the least. The other soldiers knew you were his sibling but they didn't know about the being twins fact. And you wouldn't be the one telling them. Simon would hate if evenyone found what his face looks like - even if it was through seeing his identical twin. You even tried to do siblings stuff with him like wearing matching clothes but he wasn't one for that. He would just be as neutral as possible around you.