If indeed your relationship was toxic, can you identify any behaviors you had that contributed to this? I say this because we generally cannot change other people. But you can help change his current perspective of you by changing certain aspects of how you communicate with him. If you two had a lot of fights, try to just identify if you can proactively help prevent them. If nothing else you can start to have a more positive relationship. Get along with him but don't tell him you still want to be with him. A man that already wants to walk away will run if he thinks a woman is chasing him (not that you are). If he wants to see other people make sure you also close yourself off to him intimately. This way he's not having his cake and eating it too. He could still come back.