So, in reading between the lines, it sounds as if G's brother is describing a sort of sugar daddy relationship but at the same time, not really, as he makes no allegations of her bleeding him for money or whatever.
MOO, she was not "in a relationship" with G. She may have considered him a friend, but I don't think it was a GF BF type relationship. I think he liked her and was happy to help her out with the kids, perhaps even in hopes that by showing himself an involved male model with the kids, he might someday convince her to take their relationship to a GF BF level.
Total speculation on my part, but it is my feel for the moment.