She is walking around in a confused state right now she seems to have too much on her plate to be able to handle on her own and she thinks giving it all over to God will help her to sort things out and she may also feel that if she gives it all over to God then she has to walk according to the God's laws and adultery is against God's law, I feel this is what is keeping her from you the fact that she realized what she did with you for 3 threes wasn't right in God's eyes and if he wants her to be with you then he will make a way. She is so confused that she is trying to find any kind of normality in her life and right now she feels as though God is that normality. She is probably taking this time to do some self reflection on her part to try and see her part in the situation and the things she did wrong to cause all of this and she isn't making her husband be held accountable for the things that he did instead she is taking all of the blame she needs to do some soul searching to see what she wants out of life for both her and her son. She needs to be independent and learn to love herself again. Do not be clingy towards your ex this will make her run away. What she needs to do right now is live her life for her and her son, also boost her self-esteem. She has to love herself first, be independent before she can love others. I think I told you this before about her self esteem and getting to love herself before she can be good for anyone else.
She need to learn to listen and communicate better with you instead of shutting down totally that is not healthy nor productive. Communication is essential in understanding each other, to understand why the break-up happened, and lead to the possibility of winning her back. Work towards showing her some compassion and trust so that your ex opens up and feels comfortable talking to you again, she may feel like she has no one to turn to right now and you have to find a way to show her that she can trust you with her deepest darkest secrets, if you really want to get back together again, push away all of those negative thoughts and ask yourself instead, "What is it actually about this person that I love?"
Try to approach your ex with a sincerely XXXXX XXXXX start communicating, walk up to her some time at work and ask her how she and the son are doing and if there is anything they need I doubt very much she would make a scene at work and she will have to be cordial and maybe you can get the answer that you need. You say she will not talk to you then you do the talking, tell her that you have been thinking about her and the things she has been going through and that you wish she could confide in you, she may not be taking you seriously because you have done all the talking through notes and letter and not face to face, you really have nothing to lose now.
Just try not to corner her she already feels stuck and cornered by her husband don't add to that just go up to her and say to her " I know you're confused and I don't want to add to that confusion I just want you to know you have someone to talk to is you need me and I want to be there for you and your son no strings attached maybe is she knows you aren't going to harp on the relationship she will open up more. it may not be the progress you are looking for but it will be a start to possibly communication again at least. If you are happy with my answer click the green accept button so that I can get credit for my answer and also please leave feedback on my answer.