Thank you, everyone, for your responses. I think that I need to stop focusing on the PIV aspect and just enjoy being with Him. And we talked today and recognized that we respond to each other better when we're in better shape (ie, we both need to lose a few pounds, so that will be a bonding activity for us.) LovingRadiance, thanks for the suggestions that our girlfriend become more engaged in penetration activities with me.
Galagirl, thanks also for seeking clarification. The desired outcome is being able to have PIV sex with him, hopefully long enough to bring him to orgasm. Right now, that is not happening with He and I. At all. Not when we're 1-on-1 (we live together) or in the triad. Fairly soon after entering me, he has ED.
The difficult thing (for me) is that He is able to maintain the erection with her and orgasm with Her with PIV sex. He has explained it that a part of it is NRE, a part is that She orgasms more easily (I often do not with PIV sex as a result of my hysto) and that He is orgasmic in response to Her.
The other difficulty is that this is a new development in it's consistency. Before She joined us, the ED was not a regular occurrence with me. Now it is. We do share in various oral and play activities, but I've always gotten particular pleasure in his being able to come in me, and without my orgasming. And now, I miss it.