[brudgers]

"What would be a fair distribution considering he is joining with lower risk?"

In my opinion, this is entirely the wrong question to ask. The equity for your new partner should be based upon the value they bring to the company - e.g. What is a fair valuation considering the risk of the company failing without the new founder?

To put it another way, you are bringing customers and traction to the startup. And that is your job. The work you did previously is sunk cost.

If you start your relationship fighting over percentages of $0.00, don't be surprised if the relationship doesn't end well. If you don't want to see your new partner succeed equally to you, it's better not to make them a founder.

Good luck.