I’m so, so sorry about your DF. I can’t begin to imagine what you’ve been through since he took his life.
Have you had any form of Counselling? If not, I would go to your GP and tell them how much you’re struggling and ask for some grief counselling, preferably with a Counsellor wirh experience of losing a loved one to suicide.
I totally get how you feel about your DS too. I think it’s natural to miss the closeness toh have when they’re little. He will always need you though, it’s just that he will start to build his own friendships now and explore the world a little more. Really that is a good thing, we want them to grow and that does include them growing away from us a little. Afterall, it would be a bit odd if he was 15, sleeping in your bed and you were his only friend 
It does sound as though you’re a bit depressed. You should probably also tell your GP how you’re feeling.
If you can, start to write down how you want this next stage of your life to be whilst he is in Primary School.
If you’re self employed, do you need to work all of the hours that he’s in school or do you have time to join something like a walking group? I think walking groups are good of you’re shy because you can talk, or not if you prefer, and you’re not face to face when you do talk so it’s a little less intimidating. Plus you all have a focus and something to discuss which is the walk itself.
Going to yoga in the day might help too?