I've got to be honest here. I'm sure that this was horribly embarrassing for you and probably for her as well. But I don't think it will do any damage to either her psyche or to your relationship. On the one hand if she's old enough and experienced enough to actually understand what you were doing then she probably knows that its perfectly normal and healthy and that pretty much all guys do it. On the other hand, if she's too young to understand what it is she saw than she probably thought it was weird, but probably didn't understand the sexual context of it and she'll likely forget it very quickly. I don't think anyone ever developed psychological issues as a result of accidentally seeing her brother jack off. I wouldn't be too concerned.

you didn't see that coming.... did you? that's why you make sure no one's around

clearly i cant click your life sucks...you weren't getting sucked..you were wanking

"Here I aaaaaam!" "Mpf... too late..."

Just a tad odd that OP would place this FML under "intimacy"

Sometimes I forget that FML is all around the world and not just the US

Welp, hopefully she's learned a valuable lesson about giving people their privacy when they're in private places. Not your fault.

Usually at night when everyone is asleep is the best bet...but now you know to check the closet next time

She knew.

Wait...were you just like standing in your bathroom wanking it? Do that shit in the shower, or your own bedroom.