idk if this will work for you, but I just slowly started leaving my Fandom A (like stop commenting on posts/stopped talking about it on my lj) and started being a bit more active in my Fandom B. I wouldn't worry too much about someone finding out. You're human and as a human you have a right to change you're mind and be interested in other things. If someone confronts you about it, just tell them that.
no subject
idk if this will work for you, but I just slowly started leaving my Fandom A (like stop commenting on posts/stopped talking about it on my lj) and started being a bit more active in my Fandom B. I wouldn't worry too much about someone finding out. You're human and as a human you have a right to change you're mind and be interested in other things. If someone confronts you about it, just tell them that.