oh, ps: you make the analogy of "doing it with your brother or sister". I think that is projecting something upon him that is not deserved. a "long time friend" might be fairer.
In the case of a brother or sister, there is a specific reason NOT TO have sex with them. Whereas with your husband, you merely are "not attracted to him". There's a big difference between the two. Unless there's something you're not saying? Unless there's some reason you actually feel a compulsion NOT TO have sex with your husband, rather than just not "having feelings" for him.
My current status: june 2006. Wife ran out and filed D. Finalized Jan 11, 2010, after 12.5 years M. 3 wonderful sons caught in the middle