Juniper,
If he is having that much trouble deciding what to do, then he must have "some" feelings yet for this person. He can have a healthy relationship with his son wether he is involved with the mother or not. You know your value, so please don't wait for this man to decide if he wants you or the ex. Make your intentions known to him, but don't humiliate yourself by giving him reasons why you are better than the ex...it might put him on the defensive towards her. Give yourself a time frame for him to make this decision, when time is up, if he still hasn't made the decision, then time for you to move on. I know the personal heartache this can cause, but better to get it over with now than later. Hope this turns out for the best for you in the long run !! Keep your chin up even if it doesn't go the way you want sweetie.