I jacked off to a photo of my cousin
Why would you use your cousin's picture in such a way?
She seems attractive, hot and too good to have real sex with.
Masturbating is a healthy sexual activity for some. She is your relative and that is taboo, never do that again. It is pretty much creepy and it will mess with your mind, and you might even start stalking her.
It's whatever.
I do not think that it is just whatever, it is something that you should not do. It is wrong to think about a family member in an intimate situation like that.