Regardless of the poly lifestyle, I would think that perhaps you two need to reconnect. I'm totally new to this whole thing, but what I understand about polyamory is that we aren't replacing a love but adding a love, to put it simply.
I wonder, were you already drifting apart? Had you already stopped being intimate? Did you desire your husband sexually even six months ago? Are you spending so much time focusing on the other relationships you have that you've forgotten to continue support of the one you already had? Please don't think that I'm attacking you, I'm not; these are just thoughts that came to mind as I read your post.
As for what is "normal" in a relationship, psychology tells us that after the blush of the honeymoon period that the frequency of sex falls off and eventually evens out to a frequency that suits both parties (I'm working with facts about monogamous couples). My husband and I are still intimate at least 4 times a week after seven years of marriage. There are times that falls off, like if one of us is sick, but for the most part, we're still honeymooning.
Everyone is different, so what's "normal" for one couple won't be for another.
Pinky, 41, f, bi. Married to Bear, 42, m, straight.
Not dating anyone right now.
I became insane with long intervals of horrible sanity.--EAP