I could cope because I would make it happen. If you really want something you'll cope and manage in my opinion.
So you think parents that cant cope, don't because they didnt really want the kids. Or, all, didnt really want their divorce?
I am am a single parent to 2 kids. Older than yours.
Forgetting how awful it is to trick someone (yes its tricking if you are letting him believe the marriage is working), trying to split your attention on 2 children as well as managing a household alone, isnt easy.
There no guarantee your existing child will get on with a sibling. He may well resent the sibling for taking so much attention from him.
Lots of people dont get on with their siblings even as adults. They dont add anything to eachothers lives.
You are doing this solely for you. Not for your child. If you child was your primary concern, you would be getting out of this abusive and unhappy relationship. Kids know when there is tension and when their parents are unhappy.
You are keeping your child in a miserable situation, claiming you are doing it for him.
You arent. You are doing it for yourself. No one else.