I mostly agree with you EXCEPT...they once dated and presumably were intimate. I can't help but feel that that somehow changes things. 

I'm not saying they can't or shouldn't be friends, but that factor somehow puts an obligation of openness on the table--inviting spouse along, keeping meetings mostly to public spaces, group things (when spouse can't be there, is it just the two of them, or a circle of friends, does he bring his girlfriend--does he have a girlfriend?) that sort of thing.