Don't be so hard on yourself. If you both have a history of arguing over the paternity of your son, then "sorry, I should have been more sensitive" only after prolonged texting doesn't real cut it, does it? To keep on mentioning that your son doesn't like like him sounds like baiting to me too.
It doesn't sound like he gets it, really. That is such a shame for all of you.
How is your son doing?