I would break it off.
Your suspicions about what he plans for the future are spot on - listen to your gut, here. Also, tell people you trust what’s happening and get support from people who aren’t him if you can. The reason he’s pushing to get married quickly and merge finances are to make and keep you dependent on him.
Children would tie you to him forever, even if you did manage to get divorced, and they would be used as pawns by him to keep you under his control, or at the very least, punish you for perceived infractions. This sounds extreme, I know, but it’s actually common behaviour with controlling people.