I'm so sorry.
Your DS is a credit to you. For him to share his feelings with you in that way - that is special. Many parents don't have that relationship with their children, espeically little boys who are encouraged to keep feelings to themselves. You have done an amazing job and he sounds wonderful.
I am not an expert but I can tell you that I've felt as you do. I can also say what I did to get my DS of a similar age through it:
I hugged and cuddled him all the time. Any time there was a break in the day, even waiting for swimming lesson to start etc., I would just hold him and whisper in his ear how much I love him.
I reevaluated every part of my life looking for ways to spend time with him. If we ate Cornflakes for supper, that was fine. I stopped making beds and fussing over cleaning, if it meant we could just be together instead. If I felt even slightly under the weather, sick day it was and I'd keep him off nursery for a "mummy and DS day".
I started to take him for long walks where it was just me and him.
I took him swimming every week.
I also took time to pull my friends closer to me, to talk to them about how I was feeling so that I wouldn't accidentally put my emotions on my son. I wrote in a journal a lot in order to "purge" out the terrible feelings I was having regarding my split from ex.
I am the daughter of an angry mother and I have very little patience with children in general, also little patience with myself... I worked extremely hard to control my temper and be patient with my DS during this time as well. I am now largely free of my impatience issues because I was able to change my habits if that makes sense. Learned to think before I react.
I think the main thing is to just pour out your effort onto your DS and yourself. Build both of you up. Life will come with its slings and arrows, so spend all the time you have filling his little life with love and support, that way he carries Mummy in his heart even through the hardest times in his life.
You're in my thoughts. Be strong, be brave, and get help around you in any way you can.