alma, forget your past and move on in life. If he is showing kindness, may be he wants to apologise. Take it in good stride and try to forgive. But keep a safe distance.
About his GF, I understand that you are concerned. If you know that girl, you may warn her softly but without interfering in their relationship. May be few hints would do. But please, move on in life and try to leave past behind. Do not look back. It will only hurt.