Do you really need to go into all your hurt feelings? Have you been over some of that ground before? Could you acknowledge and appreciate his apology without going into to much detail? You can reflect back what he's said and let him know how difficult this must be for him and show him some compassion. That's what he's trying to do for you.
That doesn't mean you sweep all your hurt under the table, but is it really going to help to go into all of it now? If you are really angry still, you could write a response and sit on it for awhile before you send it.
Minimally I would acknowledge that you appreciate his apology and that you can see it's hearfelt.
That he wants to be a better parent and co-parent more effectively is HUGE. So is the fact that he sent this at all.
Your call. I'm sure you'll get some good responses here.
