Nope, not at all, just that your parents may be surprised by it....they tried to make a family and make-believe you are brother-sister. If you didn't get the fantasy, its not your fault.
Fuck his brains out if he'll let you, then, without shaming yourself or anyone, decide if it was good, and it is something and someone you want in your life in that way.
If you really want it, keep it a secret or come out with it....only if it is what you like, once you had a taste.
