If he closes the LLC, then perhaps there is a way for you to recover the work you did by taking over the Shopify site, and operate it yourself. If you make it work, and wants back in, charge him $10K for a small minority share on your terms. Or not, tell him to get screwed. Your choice.
This is exactly what I would do. Hopefully the new owner takes it to levels you weren’t prepared for, and you end up making nearly the same revenue from it without working.
You’re young enough that you could take a portion of the money from the sale of the business and start something new, grow that, and sell it in 5-10 years, also retaining a small equity position. Then do it again. And again.
By the time you retire early at 50-55, you could have significant passive income from multiple businesses, as well as substantial savings, stock, and real estate holdings, and have the retirement of your dreams.