I'm afraid I must take a different approach than many of the other esteemed eHellions on here. First, I think you did nothing wrong and have nothing to apologize for. You can not help it if you developed feelings for the other man (OM) and OM can't help it if he developed feelings for you. Second, you both attempted to do the right thing by stopping the flirting you were so used to engaging in before it turned in to something more. Your DH, in my humble opinion, is handling it right. He understands that feelings are not the same as action, and does not hold it against you. OM's wife, on the other hand, can not deal with the fact that her husband is attracted to someone other than her.
Therefore, rather than confront the fact that her own insecurities are what is causing her anger, she takes it out on you. I think the best advice would be, as others have said, just steer clear of that couple for a while. You did nothing wrong, nor did OM. It is OM's wife that has internal issues she needs to work through.