She remembered Adam as an older brother.
So, when Maria wanted to get away from home, who better to go and stay with while she decided what to do with her life?

But she hadn't seen him for five years. The Adam she met in London now was a successful doctor--a sophisticated man of the world, who, after all, was not actually related to her.

Loren Griffiths was another unexpected factor. She made it clear that Adam was hers and she'd deal ruthlessly with any competition.