Regarding boundaries, he will text/ overstay when in the house. Because he is saying that he wants to try again, I now feel that I’m breaking up our family which, I know, is not true but all the same it’s just a horrible thing to experience.
The reason you’re feeling this way is because he’s continuing to get what HE wants. He’s suffocating you and he’s calling the shots. @poetryandwine is right, these contact arrangements with your son seem to have evolved from the desires of your husband?
He still sees you FOUR times a week where he overstays, applies pressure and guilts you into staying with him. He’s still visiting your son in the house (which should be your private space right now) and he’s still texting you a torrent of daily bullshit.
Until you put a firm and final stop to this, you won’t get the space you need to process anything and think about your next steps clearly.
If possible, your husband should be picking up your little boy and taking him elsewhere to give you space/child free time. He shouldn’t be waltzing into the home four times a week to play happy families/berate you/cry/guilt trip you/plead/whinge/whimper.
Alternatively, take yourself away when he’s in the house and have a trusted family member or friend to facilitate contact with your son.
And echoing the above posters, go and see a solicitor. At least make an appointment? You need expert advice right now and it will honestly do you the world of good.