Ask HN: Co-founder quitting. What shall I do?

Hi HN, For those of you who've been through it all, I would love to hear your advice. My co-founder has decided to focus on another career path. While I've found another guy who's interested in helping me, I'm worried that people would just come and go without sticking it out for the long haul and potentially take away the equity. That being said, we haven't officially formed a company so I am not sure if my co-founder is entitled to anything? Also, I'm determined to keep moving forward since we've been seeing some promise but at this stage, would it be a good idea to take on a co-founder? I can see a need for a more technical one but most people I know have stable jobs and aren't likely to pull nighters and weekends. Thanks for your advice.