[nkallen]

I know exactly what I would do in your situation.

Tell the CEO you need to go to Thailand for 8 weeks to chill out. Avoid quitting so that you can keep your Visa. Strongly consider going to your primary care physician (cheaper than a psychiatrist) and get on an anti-depressant. (This will hard to do at the same time as leaving a country as your doctor will likely not give you a two month prescription to start.) Bring your GF with you to Thailand for some of the time unless you are comfortable traveling alone. The travel experience may be enough to get you out of your rut, but I would get on an anti-depressant as well. Also exercise. Twice a week is enough.

Ignore anybody who tells you to "deal with it" or "subsist". There is more to life than your first startup. Learning to cope with depression is a lifelong process and isn't solved by just sucking it up. Also depression is not really a unique and beautiful snowflake of a disease. A change of scenery and anti-depressants will work 90% of the time.