I've been through a handful of ventures in the past few years with ultimately no lasting success. Some made money in certain periods, but ultimately they failed, with the thousands of hours and many thousands of dollars invested in these ventures now "down the drain".
The only thing we can keep doing is pushing forward. Failure must be seen as a learning opportunity, not a failure of intellect or similar.
With that said, if you are experiencing emotional side-effects, which are completely normal from my POV (I've certainly had them), I urge you to consider your mental health, nonetheless your overall health. Success and money do not mean a thing if you cannot get out of your bed or house every day, or if you've frayed all relationships (whether familial, friendships, etc.) while working as hard as we're told to as entrepreneurs.