Your only responsibility to his wife is to make your preferences known to everyone. As far as community goes, being public with your private relationships is entirely up to you. There are a lot of people that are open about being poly, and a lot that only mention it to people they're interested in.
Leaving things exactly as they are sounds like a recipe for someone getting hurt. If his wife can't accept that you don't want to be friends than she'll get hurt, and if she's hurt than your boyfriend is likely going to be hurt as well. If you force yourself to be friends and it bothers you than you'll likely just grow to resent it, and things won't work. Those are the extremes, but you can see how a lack of communication doesn't help.
By talking with everyone you won't guarantee that things will work, but maybe his wife wants to be friends but can accept that you're not interested. It may still result in things ending, but get it all out in the open so everyone involved has the chance to make their needs known.