If you're experiencing wild emotional swings:

• Find some form of therapy to deal with the emotions. Even if it's just going to the gym routinely, exercise and having a ritual to look forward to is great at blunting emotional swings. Executive coaches are underrated, as are regular lunches/dinners with other founders. You're not alone.
• Find the triggers for the highs and lows and create systems around them to help mitigate the major swings; chances are the things that trigger you are aspects of the business that have been left unchecked and need fixing or codifying, good or bad.
• Contentment = clarity. Celebrate the wins, acknowledge the defeats, and move on. You don't need to be perpetually happy—happiness is supposed to be fleeting. A high baseline level of contentment is a valuable tool because that's where you reset to after a high or a low. The more content you are in general, the faster you reset and the less drastic the swings are. This takes work, but is rewarding beyond your career.
• Talk to your customers. Talk to your customers. Talk to your customers. If you're very far removed form the end user, of course it's going to feel overwhelming. You have no idea what's working unless you talk to the customer.

As for whether you should stay, your gut probably knows the answer to that already. It might not be a yes or no question; what variables can you change to make your work and life easier or less burdensome?