Sorry to hear that you're going through a tough time. This forum definitely has lots of great information and stories to draw from.
Had you considered polyamory before your husband or is this your first go around dealing with your partner having a more long term relationship? Like you said, he's done a lot of legwork so hopefully he can extend you some more patience and kindness so that you can do your legwork. How is the relationship between you and her? Are you close at all? Poly can be very very stressful and bring up a tornado of emotions. Certainly, it can be very rewarding if you manage to work through some of the stuff but it does take time. So, don't feel down on yourself for not immediately being totally ok with everything. Sometimes a therapist can help to sort through this kind of stuff.
He's also in the throes of NRE most likely and that can be challenging for anyone to deal with. Why were he and his SO trying to 'shake' things up on social networking? Like activism or something? I can see how that might feel a bit hurtful even if they didn't mean in that way. Do the three of you go out in public ever? Maybe the three of you could go out and all hold hands or something, a way to shock and awe but one that includes you as well. These things you're describing sound like a lot of people's struggles with poly so don't feel alone or abnormal
. You sound like you're working very hard to give him what he needs and wants in this.