Hi...
It is true you are not a child anymore....
But..
You also have to understand.....your elder sister...is your
elder sister......
She is not your friend or someone like that.....
So......because she is a family member....her position and her
relations to you....is within the inner ring of family
relations.....
She is just thinking about your well-being....
Due to that, she may be shocked and uncomfortable when she found
out the condom...
Well.....to understand her feelings, maybe you can imagine a
similar scenario in reverse....
What if you find a dildo and birthcontrol pill or abortion pill
in your sister's room.
How would you feel ?
Would you feel completely normal, "she is an adult already not a
child, I shouldnt interfere, never mind"
Maybe to understand it further, imagine if she is your "younger"
sister.
I say that because older siblings have stronger inclination to
protect the younger siblings.
Well.......
It is an uncomfortable situation for you also.....what I suggest
you do is......to keep quiet and to be passive about it.....no need
to justify anything and no need to talk about it......
I think you need to protect the siblings relations / family
relations and keep it intact......
Sexual matters is taboo and uncomfortable and personal......and
its hard to cross over or bring it into the family relations
matrix......
So my recommendation :
Keep quiet and let it slide.
Next time be careful and be more discreet.