Depression can also be a result of having AvPD. Makes sense if you think about it - if you want social connections but can't have them, it will get to you after a while.

One way you can tell the difference between depression due to a brain chemical imbalance and situational depression is, if medication works, it's the former, and if it doesn't, it's the latter.

Another way to tell is to make changes to whatever situation is causing your depression and see if it improves. Change your stressful job, ditch toxic people from your life, figure out a way to improve your financial situation, do rewarding hobbies, etc. If your situational depression is due to an AvPD relationship Catch-22, unfortunately you're basically up the creek.

And the two variations aren't mutually exclusive. You can have both types of depression at the same time. If that's the case and it's not a result of AvPD, a combination of medication and lifestyle changes can tamp it down.