I thought a quick update would be helpful.
We didn't have a veto rule, but F became increasingly uncomfortable [her words hurt] that I was actually enjoying the relationship with E and that F wasn't an active part of it. I think this suprised her as much as it suprised me, and so, as he often does, she changed the rules of our engagements. more about that in a minute.
So I've had to change the relationship with E to downgrade it to a friendship, not lovers. It seems that the only part that F has a difficulty with is knowing that I might fuck someone else and she not be a part of it. For F there is a distinct sense of belonging that she doesn't want to get past. However that also means that she is looking to find ways to make it work where she doesn't feel she looses that connection with me. This seems to be very similar to feelings that I've read other people say on this forum, so I'm taking this to be a good sign.
The new rules then are: Not to look for an ancillary relationship in MK. (thankfully F is happy for me to continue seeing E as a friend, and E seems open to that - which is very magnanimous, because I do feel like I'm messing her about a lot!) Meanwhile F and I are going to look for people to include with us and attempt to date as a couple. I think this is a little more like swinging with friends, but it's where she's at and I can't really rush her with this.
F seems open to putting herself in places where this can happen too (dating sites, clubs, poly meets) so I'm hopeful that it's not just a knee jerk reaction designed to slow everything down, but is a step towards finding what will work for us in a poly way.
F has closed down her OKC page again, saying that she doesn't want to do that on her own. That makes a little more sense to me, given what she says she wants and doesn't want. 3 weeks I guess is a long time in poly life.