Dear brothers n sisters in Islam. I am a 23 years old male, and currently in a serious relationship with a girl (my classmate).
One day, while we were hanging out, it is our own activity to play with each other's smartphone (just for fun generally, to check for any suspicious messages from opposite genders' friends and to make other jealous, joke around etc.). We are very strict in term of maintaining distance between us as well as other restrictions because we fear that our relationship might not be blessed the Almighty God (God forbids), so while playing each other's smartphone, if for example I want to open a certain apps on her phone, I would ask her permission first (in fear that there might be pics of her or her female family members exposing their aurah and whatnot).
I was scrolling through her Telegram chat n there was a chat between her and her female bestfriend, I asked her if I can open and read their conversation, she said no problem. Thing is, she might forget this, but upon scrolling through their conversation, I saw a glimpse of her pic without scarf, so for a split second I saw her aurah : her hair.
I frozed and was extremely scared , but I covered it up because if she finds out, she might be extremely mad at me and it'll probably ruin our relationship with marriage goal. After that incident, I felt very disgusted with myself and I can tell that I just made a huge huge mistake, though unintentionally, but it was a very big sin that I committed that I almost threw up alone in my car when I remember the incidence.
My question is, what should I do? Did I just commit a big sin and should I tell my fiancé regarding the matter?
Thank you very much in advance dear brothers and sisters , very sorry for the long explanation.....