Thank you so much for your thoughtful and sincere reply. It is very much appreciated.
Since finding this forum and posting this intro post I've been doing a lot of lurking and am finding it extremely useful. So many people posting here are so deeply aware, open and honest. I've not felt the need to post again because there is so much learning to be had just from reading the many words of wisdom that are already here. Thank you, to you and to everyone for sharing so forthrightly here.
The one thing that has become clear to me from my reading - about so many, varied relationships and situations - is that I need to really figure out what my needs are and to communicate them much more clearly to my partner. The depth of emotional honesty needed to make poly work is much more than I think many mono partnerships have. It's easy to cruise, to begin to take things for granted a little and I think that maybe that's where we are. We haven't challenged ourselves to look at our partnership, to pick out the bits that maybe aren't working so well any more (and celebrate the bits that are) for a very long time. There's no blame in that. Day-to-day life, raising kids, etc is plenty enough to be getting on with and when the basic relationship is solid enough it's easy to leave it in a corner knowing it's solidly and reliably there, even if it starts to feel a bit flat after a while. I know now that addressing that is where we have to start and you never know, I might find that once we've given ourselves a bit of a shake off that I feel much more settled with the idea of long term monogamy again. And if it doesn't, we'll have a much stronger base to start exploring alternative options from.
We have a child-free night in a hotel coming up next weekend, so I intend to raise this then. I also think I'm going to get hold of a copy of 'opening up'. I'm in no rush here, and wherever we go next it has to be right - for us. Once I'm over my initial anxiety about challenging the status quo I think I'll enjoy getting deep and meaningful with my partner again. I just need to approach it in a way that doesn't threaten or upset her. That's my challenge. I've been known to put my foot in it before by wording things badly. Hopefully all this forethought will help...
Thank you again for your reply.