Michael, the advise that I feel someone should give you here is that while each of us has free choice, inevitably in our lives there are times when our destiny is shaped by things outside of our control. This may be one of those times for you, and my advice is to keep your resolve to be a better person regardless of what your girlfriend decides to do.
Prayers for her to return are not what's needed. Thoughts and prayers that you find the strength to improve your life, regardless of the twists and turns that life has given you is what we should ask for.
I do not say this lightly. I know you don't want to hear this, least of all from someone you know so little. Believe me, life has a strange way of making the correct path very hard for us to see when we are walking, sometimes in the dark, and cannot see beyond the foot or two in front of us.
Those strong in faith like to say The Almighty does everything for a reason, and to call upon your faith for that inner strength. That is what I shall pray for, you to have that strength. Stay strong, if it's meant to be she will return and if she does not, you will need the strength to keep from spiraling further. STAY STRONG!