It's against the rules, yes.
However, I share an account with a friend that I've known for 2 years (Nothing has happened yet) in the past yes, but if you stay low profile & don't do anything major & stupid, you'll be fine.
Also a good tip; Don't say to anyone/public chat or any sort that you're account sharing/the account isn't yours. (I know this is a no brainer common sense rule but many people blurb it out without giving it a second thought).