This has happened to me.
When DH and I moved in together (1 bedroom flat at first, we couldn't afford more, but did have a sofa bed) the ex said that she would only allow overnight contact if my DH slept on the floor in the living room while DSS was in the sofa bed.
Who the hell was she to decide where myself and DH sleep? Did she honestly think we'd be having sex in front of him? Or at all?
So stupid and vindictive. Don't be like her.
I wasn't very comfortable with it but between the ages of 4 and 6, DSS would often end up in our bed in the middle of the night. I was uncomfortable because I knew his mum would go mental and stop contact.
As soon as we could afford it, we moved to a 2 bed, and I encouraged DH to take DSS back to his own room and give him a cuddle in bed there if needed.
What I'm trying to say is I know it must be really painful for you, but as long as your DS is happy and comfortable then there's nothing to worry about. Forcing him to sleep on his own if he isn't used to it will be worse for him.
You cannot stop contact because something has upset you unless it's a serious danger to your child. To do so is to use your son as a tool to hurt your ex. You have no right to do this, you need to put him first and not yourself.
DSS is now 7 and we've had years of trouble where his mum stops contact because she's angry at DH (when I got pregnant, when we moved in together, whenever he refuses one of her crazy demands...)