Thanks for your response.
I know the circumstances are not what people advise. But that's life, I'll have to deal with the way things developed.
We actually define the relationship as broken but simply can't afford to but a second home. Renting is almost impossible in this town. We live in a gresat neighbourhood with many friends literally next door, our kids go to a brilliant school around the corner - most of the time I feel that the situation at home doesn't make me suffer 'enough' to make me give up all that. If this relationship was physically or emotionally violent, this would be different, but we are friends and get along well.
But of course, this is the reason for my first sentence above. I'm not sure whether this counts as poly. We do care for each other, but we are not in a romantic relationship any more. So basically we are just friends.
Re: being open and understanding: I've tried for ages. He just doesn't want to talk about sex. Neither about things he might like, nor about things that don't work out (e.g. his erectile dysfunction - and trust me, I was really really careful when trying to talk to him about this). I can't reach him. And after five years, I don't want anymore, it hurts too much. And again, sex was just one of several issues - no more but no less either.
So we talked about getting divorced and moving away. Then we realised that (at the moment) we find it easier to give each other the freedom to have other relationships and still parent together and be with each other on a platonic basis. We might decide otherwise in half a year, but this is our idea right now.
And now I wonder: How can we let other people into our hearts when we can't bring them home? Maybe a small appartment will do? Does this all sound too pragmatic...?