I also think of this as thing you have to do for a good friend. Perhaps try thinking of it as a job you have been tasked to fulfill (eg standing up for your friend, witnessing the marriage certificate, holding her bouquet, making sure none of the guests get unruly, etc) rather than a "party", if you fear you will be miserable.
As for your husband, could you ask the Bride to seat him with some people who can make him feel welcome, and talk to him?
I know you have the option of stepping down, and letting the Bride know that you and your DH would simply like to attend as guests, but I personally think that should be a last resort. YMMV, but I'd personally be a little hurt if my best friend did this to me, without any explanation whatsoever, etc.