I want to dump him, but I don't want him to date anyone else.
Why don't you want him dating someone else?
Because I want him to know that I'm the best person he will ever have been with.
That is not a healthy attitude to have about a partner. If you're going to break up with him, you should be fine with him seeing other people. It's normal to move on and date other people after breaking up.
I don't care what's normal. I want him to be obsessed with me after I break up with him.
You shouldn't want someone to emotionally suffer so much after breaking up with them. Wanting him to only be with you, but refusing to date him is unhealthy and very rude. You should let him move on with his life.