Your girlfriend couldn't get past needing to look good and acceptable to the world. It isn't that she doesn't feel anything for you or the kids. She is afraid and she has been taught to see God as hating real uplifting and honoring love between gays and lesbians. Yes, I know it seems as if she has done this to you personally, but she in fact, is not happy or comfortable with her life. Her leaving had very little to do with you and everything to do with how she sees herself.
People do harmful things to themselves and others when they are afraid and feeling trapped.
The power and control that legalist Christians exert is just too much for some folks. She may not come back and, yes, you only can trust God. Trust God, my child, to be with you in your pain, your despair. Be open to God's direction, listen for that still, quiet voice of God that will bring you forgiveness and peace. You are not alone.