Well done on seeking help. A lot of people never have the courage to admit there are problems. You are a long way to fixing things and getting your life back by taking this important step.
Now you have to tell your (letter or email) what your therapist has said about the situtation ie that you need the break and no text, or midweek contact etc. He can't know unless you tell him exactly how it is. Don't keep this to yourself, it is important he understands this and that you need to find closure and deal with the relationship being over. If he doesn't believe you then ask your therapist to speak to him to confirm what you have said.
Which bed your child sleeps in and if they still has the cough sounds like a parent who is anxious but hasn't moved on and accepted that he is not able to have that every day contact any more either.
Remind him that you will contact him if there is something significant that he needs to be informed about, but that everyday things in your time, while he might want to know, he doens't have the right to intrude on you about them now.
Fix a day midweek that he can phone and speak to your child, and don't speak to him yourself during this conversation. Give your child the phone, walk out of the room so they can say whatever in peace, and then when they're done hang the phone up. Explain to him that this is what you will do so that he doesn't expect to speak to you and doesn't have a fit when you hang up without speaking to him and use it as an excuse to call back...
If he has things he needs to discuss with you then ask him to email them to you and you will respond when able. Urgent messages such as delay in arriving for contact can still be sent by text, but asking how his cough is etc should go in the email. Respond to the emails once a week.
You have to think of yourself and your needs, not pander to your ex's needs here. It is not in your child's best interests for him to be texting you like this, infact it has little bearing on your child at all, simply your ex can't let go and wants to be involved completely. Lovely as this is, unfortunately the circumstances are now that you live apart and he can not have that everyday contact and conversation as he would if you were together. Explain the situation, give him fair warning, come to a compromise, and then stop answering his texts and phone calls at times other than those agreed.
You need to do this for your sake and for your child who needs a sane and calm mother.
best wishes
Gilly