Music groups tend to have the same issues; it's rare to find a band like U2 that equally shares credit regardless of who is doing what, which normally builds resentment when one or more members are seen as sole contributors (or 'stars').
It's also equally rare to find a group where each member can split off and form their own successful group (e.g., The Beatles, Genesis). The 'right' answer is that's it's usually somewhere in between. Freddie Mercury and Mick Jagger failed at solo careers because they didn't have their friends to tell them that their music stunk. Of course Top 40 has been broken into a formula that primarily benefits music companies, but that's different story.
In the same way, you and your business partner may have relied on each other to achieve a whole that is more than the proverbial sum of the parts. Your partner's new venture may fail without someone such as yourself, since it really is a common blunder by technical people to underestimate the value of sales and other soft skills, and your venture may fail without strong technical backing.
As usual, you can throw money at the problem to see what works, but in my experience when people 'grow up' organically as opposed to in a lab, the resulting bonds are much stronger.
All of that said, my former business partner surreptitiously formed another company and lost interest in our shared venture, which ultimately killed what was a great niche product. I consider myself a fairly average coder, but he was brilliant, and although I could have bought him out and maintained and expanded the codebase, it wasn't fun anymore, so we sold to another company and went our separate ways. Regardless, I had fun and learned a ton along the way, and that's part of the journey.