Trying to fill the void when you're in a rush to get into a new relationship or desperate to get your old lover back gets in the way of a healthy separation. The Buddha taught that attachment causes suffering. Therefore, the direct path to happiness and peace is separation.
There is a short parable about an old gardener who turned to a monk for advice: "Let me ask you, 'How can I feel liberation?' The Great Monk replied: "Who bound you?" The old gardener replied, "No one." And the monk said, "Then why are you seeking liberation?"
When sadness fills your heart, repeat the mantra: "I don't need anyone or anything to be happy." When you're grieving a loss, it's hard to believe that you can be happy without that person in your life. But you can. It is creative work to fill the void that has arisen, and you are capable of this - with the help of your inner strength.