I've posted this kind of answer a couple times:

I started ZeroTier (www.zerotier.com) initially alone. Being a sole founder is tough for many reasons. The biggest one I've found is not so much time in the raw sense but cognitive load. There are so many things to pay attention to at once: fund raising, economics, product dev, HR, engineering, devops, talking to customers, ... it's endless.

Then there's the standard issue rollercoaster of entrepreneurship which you have to weather alone. Some weeks it feels like ZeroTier is going to conquer the world. Other weeks I feel like "wow I'm an idiot this is doomed." I've learned to just ride that up and down thing and always apply a consistent forward pressure no matter how I feel.

Paul Graham always harped on single founders being a bad idea and in general I kind of agree with him. It's a tough thing to do. Doesn't mean it can't be done though and there are lots of success stories. There are many reasons you might be solo. In my case it's because I founded ZT after just moving to the area and developed it alone, so there wasn't a good co-founder. (Just picking a co-founder for the hell of it like getting married by Elvis in Vegas to someone you just met. It's a worse idea than going solo.) If you are solo just count it as one of your disadvantages (every team and venture has them!) and therefore something you'll have to work around/through. Honestly founder drama is way worse. Being solo means you get the problems of solo but in exchange you get to pass on founder drama.

One of the best things I did early on is to move into a co-working space. We are in LA/OC (SoCal) and are here:

http://peoplespace.us/

It's a friendly hacker space with many tenants from other small startups to consultants and solo people. Lots of events like code camps, maker meetups, and OWASP meetings are hosted here too.

Being at a co-working space makes you feel like you're not totally alone, especially if other entrepreneurs are present. If you have some in your area (most major cities do these days) then I highly recommend using one. If there are options other than the larger franchise ones like WeWork I'd recommend those since they're more likely to feel like a community.

(There are now four of us but we're still here. We occupy a corner office upstairs.)

Other things I highly recommend include talking to other entrepreneurs and independent consultants who are in the same boat. Then there's the basic health stuff. Exercise, eat well, and get enough sleep. Bad health practices can wear you down quick. Imagine you're an athlete trying to keep up on training for your career. You are, but your muscle is your brain. Keeping your whole body fit keeps your brain fit because it's part of your body. The myth of the out of shape genius nerd is just that. Being out of shape makes you less intelligent.

Finally if you are really feeling symptoms of depression go see a psychiatrist. Depression can be biochemical and we have good fixes for that available. The stigma here is silly. If your feet hurt you go to a podiatrist. If you have an issue with your brain you go to a psychiatrist. The brain is an organ like any other and it's one of the most important you have. There should be as much stigma about seeing a brain doctor as there is about seeing a foot doctor.

Edit: if you are in SoCal stop by and visit! My contact info is in my profile.