I think you fell for someone who had not yet showed his true colours,the comment about his ex only shows that he still had baggage.
Your right 23 is not a child,and yes I would have some questions about the comment,I would not be happy at all,BUT you did apoligise,and he was not willing to accept it,or discuss it,there's the difference between a mature adult and manchild.
5 months is not that long,and at 40 I would think as you that this is a grown man he's not about to act like a horney teenage boy... but alas,that's how it went.
Try and pick yourself up,this one is over and you have learnt a valuable lesson.
There will be another chance for love.