Ss, I told my close friends within a few days of BD. Prior to that, no one except my mom knew that we were having problems because we had always agreed that we wouldn't take our problems outside of the marriage. However, since the S I've been pretty candid with my friends about what's going on, as I've needed their help to process what's happening. Of course, my friends also know that my goal is reconciliation, so everything that I tell them is received in that context.
We tended to have friends as a couple too, but the friends were usually mostly "mine" or "his." I think it was pretty clear to each of us who we could count on and who the other person would be seeking out for support during this time. I will say that I did "take over" one of "his" friends post-S, but I warned him at BD that that was going to happen because she's in a similar situation with her H and we would have more in common moving forward. H didn't object and the friend has even commented that he is distancing himself from her.