Being up front (meaning talking about ideas before they become plans) is always a good idea.
It takes a bit to get over the sense of loss. I'm the poly one in my marriage-and I still went through that when Maca got a girlfriend.
I like to leave him a love letter or something special when I go, somehting that will remind him that I love him TOO, that he's not forgotten while I'm gone.
I also like to bring him back something-a card, a small gift that I picked up while I was gone with GG. Just lets him know that GG and I aren't pretending he doesn't exist, we're loving each other with full understanding of my love and commitment to him as well.
"Love As Thou Wilt"