You guys have been together for 8 years and there's no sexual feeling towards him... I had that after 7 and a bit with my ex-missus. We're both a bit on the young side to be in relationships where there's no sex after such a short time. Yeah, I also can draw a parallel with the friend love thing too. I think love does change, but it's supposed to stay somewhat in the realms of a desire to be together. You don't want to stay, so it's already on a loser.
So my advice is this:
Do what you need to do to make you happy. Nobody else can do that for you. And don't concern yourself with what other people think, their opinion is not important right now!
I'm guessing this means you'll want to leave him.
Basically, you need to muster up all your courage and strength, tell him to get the f**k out of your life, and move on without him. It'll be harder to do with having the little 'un to worry about, especially if he wants to see his dad, but you have the advantage that you're single, you're not tied to him, you CAN just leave! Try working on a plan of how you're going to go, and prepare something in case you need to counter any application for custody. My guess he won't bother, cos he most likely sees you as the mother and can't be arsed with the work required to raise a child properly. But in any case, make notes of the blackmails, the violence, the shouting, all that stuff. Maybe it can't be linked definitely to your condition, but if you were diagnosed after you started seeing him, it might just work in your favour! Anyway, a friend of mine lost custody of his kid to his ex wife, and she's a right head case, so you should have no problems at all! Oh, and since he's the legal father, once you win custody you can get the CSA to force him to pay for Eth's needs if he gets arsey. I don't mind the CSA when they stamp on fathers who should do the right thing.
It sounds to me like Rik doesn't want you either, but he'd rather you didn't have anyone else. This is a power thing. My GF has the same problems with her ex-husband. I can see the pattern, and I'm pretty sure you'll get hassle off him in the future as a result. And don't be surprised if he tries to poison Eth against you either.
Please, DON'T TRY AND DO THIS ON YOUR OWN!! Make sure you have friends and (if possible) family around you. It takes a lot of courage to walk away from a guy like this, and you'll be too mentally exhausted to maintain your strength if you go it alone. Keep talking to people, let them keep reminding you that you've done what's best for YOU! I'm here if you need me, any time.
Sorry if this all sounds a bit doom and gloom. I'm not gonna dress it up, I'd rather you went into this with your eyes wide open, you'll stand a much better chance if you have an idea of what you might be up against.
Stay strong, honey. I know you can do this, I believe in you. And I know Eth will be just fine as well.