I have also experience close to burnout and recovered multiple times, in the process I have lost very precious relationships, and entire years were spent in darkness. I also have friends who have been in tech for close to ten years, and are close to burning out though they would never admit to such. This is the nature of the beast, all things that appear glamorous on the outside ( Hollywood, Finance, Tech, many nonprofits) is very rotten on the inside.
You can't change the past, but you can recalibrate your expectations and medidate on what went wrong. Here are some thoughts, and I will be very harsh:
1. Your co-workers may be amazing, but they were never your friends. You ran a business and rented their years to help them build a nest egg, of which you would claim the majority share had it hatched. Alas, the business failed and thus, you no longer add value to each other's lives. Move on.
2. There's what you love, and there's what you do. It's best to keep some distance: because no one cares about what you love. VCs are vultures and this is well known, but they are also reflecting the reality of the market. In the market you're just a vendor. Think about all the food stands that you have walked past in your life, within each stand is an immigrant family who slave away for decades hoping for a better life. Have you ever thought about them and gave them time/money for their suffering? No, you only cared them inso far as they can cook for you. This is how others saw you.
3. Big companies, and indeed most big institutions is made by a silent majority of the defeated. Many have experienced what you have said and have long made their peace. They found joy elsewhere, and found distance between themselves and their work.
4. Find self worth and self-love outside of your role in the machine, there's the product you produce to trade time for money, and then there's you. They are different things. Imagine Instagram influencers who post pictures of themselves but feel depressed when they don't get enough likes. This is you right now, you're looking for external validation from how big your integer is in some database. You have to look elsewhere.