I'm concerned that you are only 21, married, and have no sex life or attraction to your husband. I agree with the idea of reevaluating your marriage.

If you love your best friend, don't do this to her.

Also, in your first post you wrote that the chances that anyone would find out about this are slim. Please don't believe that. It's not like you would be having a random affair with some guy you met at a club that no one really knows... this is your best friend's husband. The chances that someone would find out are pretty great, considering the closeness of the relationships involved.