He could be a co-founder. You have created some value. That is your achievement. But, do you want him to be to a co-founder? Does he have complimentary skills? Will co-owning the business mean you can achieve more, with the same resources?
Some partnerships end up adding up to 3 when you add 1+1 together. If that would be one of them, it's worth considering it.
What kind of business is it, and what is the exit plan? If you're running this as a profitable business without the intent of raising VC, you could get him to buy part of the equity at market rate (part of the payment could be deferred). Or you could 'sell' him half the equity, with vesting in place, but defer the payment by reducing it from future dividend payments.
Lots of possibilities, but in the end it depends on what he'll add to the business and if you are comfortable working with him.
As a friend of mine once put it, is he a creator of wealth or a taker of wealth? Most people are takers.