I thought I was depressed but then I got divorced and realized my depression was situational from being in an awful relationship. Consider causes like this as well, it is hard to see when you're inside it.
Also be careful with reaching conclusions too quickly. I ended up breaking a 10+ year long relationship after thinking that was the problem, I ended up even more miserable than before. Begged her to take me back after some years, and luckily we're happily together ever since and still married :) (with lots of changes from the first iteration, obviously)
Wow, without sounding sarcastic, that sounds like a healthy relationship! It really shows maturity to own up to it and choose each other again. Hoping the best for you both :)