Is it time to let this business go? Am I failing?

Appreciate you guys taking the time out to read this long winded post. I've been a long time reddit reader but never posted before. There are a lot of smart people in different fields giving advice based on their experiences on here, and probably even more people like myself reading these posts so I figured what the hell - maybe my dilemma will help some readers one day too.
I've been in my own head so long about my current business and have trouble speaking to people about it because most people can't relate or understand. I also don't like to burden anyone with my concerns because as we all know, there are plenty of people in the world with problems much worse than ours.
With that said, I'll try to sum up the gist of my situation as best I can -
Six years ago I was working in finance for a big corporation in a different state than my family. I ended up agreeing to leave my finance job and come run "the finance/marketing" side of a car business a couple of family members were in. I knew absolutely nothing about cars, selling them, or fixing them/flipping them.
Long story short, I tend to love to learn all the aspects of any venture/company I'm involved in. Over time, I observed and learned enough to start buying and selling a few of my own cars at the dealership. Then I eventually agreed to become a partner, take on a third of the expenses and buy a lot more units.
Besides being a partner though - everyone agreed that the business would operate best with me handling the day to day of the business as well. I do the sales, I do the title work, I do the finance deals, I even leave the front to head out back and wipe down/detail vehicles if I have to. I don't give a shit frankly - my mentality was whatever needs to be done, I can do it until we grow enough to get more help around here.
Fast forward to today, I'm completely worn out. The numbers have largely been solid, but there have been so many points where only my cars on the lot were selling, my partners either struggling with bad units or just not buying enough units at a time to be profitable - playing it too safe. All that has put a lot more burden on me.
On top of that - I did probably the most idiotic thing you can do in our business. On a busy day recently I waived the cashier check requirement on one of my units and allowed it to be sold to an old man paying with a business check. He had a ton of documents on hand and I was closing out a couple other deals and said we can waive it on this one let's just get a copy of all his documents. Of course the old guy turned out to be a felon who's been charged with fraud and identity theft before and his check bounced. So far it looks very bleak for me getting that money back or that car back, and I have no one to blame but the idiot writing this post lol.
In summary, I just feel like I don't have it to keep this thing going this way. I absolutely fucking hate the idea of quitting... at anything. But to be an owner, operations manager, salesman, finance manager, title clerk, and source my own inventory every single day - is becoming a hell of a weight on me.
I'm starting to fuck up (look no further than the laziness and stupidity of accepting a business check from what turned out to be a felon), my health is worse than its ever been, I feel angry/resentful some days, sad and disappointed in myself other days.
But I have fell in love with the car business. I know that I can do it well, and my numbers are actually still solid. And I don't know how I'd live with myself if I felt like I quit at this.
I'm just not sure this is the right situation or the right structure. And that bounced check and stolen car feels like the final punch in the gut. I have never done something that dumb and that costly in my life.
I'm just not sure if it's time to let go.. I know only I can truly know the answer to that question, but shit right now it feels like I don't know shit about anything. Feels like I'm just in one of those dark, empty mental spaces.
Sorry for subjecting all of you to all that rambling. I guess I just wanted to vent and hope to get a couple of insightful responses in between all the people that will rightfully come on here to call me a complete moron about the business check LOL
Thanks guys.