in a relationship, it means to forget your ex, forget about everything you two did together, forget about what you two shared, and simply tell yourself that your ex will never come back to you. As you do, go on and find things that will/may give you happiness. Focus on your own life and don't ever think about your ex, that she/he may upset when she/he knows that you do something that may not appreciate him or her.
hangout with another guy, while your ex is watching, or in his presence. This action shows that you leave the past and just go on with your life