This is kinda gross, but I've been jacking off to my much younger cousin's instagram posts
That's really not okay. What do you find interesting about doing that?
I like her face. I don't want to stop following her.
Attraction can sometimes be unexpected but you shouldn't act on it. It is wrong to do that to a family member and people will think that you are a pervert.
Yeah I wasn't going to do anything, I just liked the way she looks.
Even just masturbating to your cousin's picture is wrong. You should stop visiting her Instagram page, and keep some distance between you. If the urge continues you should probably get some help before it gets out of hand.