Well the right reasons for me would be because she WANTS to be with me and is 100% COMMITTED to me. I'm not interested in being anyone's second choice.
What would need to be different with her moving back is that we are working together on saving the marriage - not just me doing all of the work. I'm not interested in sibling type relationship with her. After two years of not really having a partner, I am ready to move on either with her or without her. I can't do that if she is living here as a roommate.