Actually I don't think I would do anything different except look for the warning signs. Her main reason for quitting loving me was when my brother got cancer and passed away because I wasn't paying enough attention to her and because I was focused on him and myself during the grieving process.
That is a horrible person. Mine started detaching from me when I was paying too much attention to my little kids instead of her. Oh, wait, they were her kids, too! And they weren't older: a baby and a toddler. And she neglected them to pursue her teen romance offline from us. Despicable.