I agree about your daughter needing to look after herself. Your husband is at peace about it. Your comraderie with your exhusband isn't so unusual. I know of several situations, myself included, where after the dust settled and time marched on a friendship grew and/or maintained despite the divorce. I share three sons with my ex husband. He's towards his mid 50's now, has had a health scare a couple of years ago, where to all of our surprise I grabbed the kids and arrived at his hospital bedside. He recently lost a younger sister to a heart attack. His father died young, when he was very young from a heart attack. My ex made his end of life directives clear to me recently, after his sister died. His immediate family wouldn't protest that, as I'm not just an ex, I'm the mother of his children.
As far as a source of support, there's things like talking about our kids or if something transpires with my immediate family, I can turn to him for understanding. I've no interest other than a sense of family, like a brother. I understand what you yourself are saying about the friendship that you have. Life is too short.