Natural??? I don't mean to seem a bit put off, but if you go into a GLBT forum and ask if this is natural what answer do you think you are going to get? Or did you come here because you wanted to ge that answer. Well here it is.
Yes it's natural. It's not necesserily natural for all people, but those who it isn't natural for don't have those impulses. So your bi-curious with a pension for being a top, you are by no means a rare breed. So don't worry about your impulses, they aren't evil and unnatural.
I suggest you go on over to the How-To Board and look for a thread entitled "Straight Males and Bi-sex" or something on that order. I think it's still on the first page.
Share your fantasies with your wife or do you think she is one of those people who would freak out. Mabey she will understand and guys could do something together like a MMF threesome. I would hope if I had a husband he would tell me all his fantasies and I could help him out.