Well it took me a while to think about what I wanted to write to you. I still am not sure that I will get my point across.
First of all changing friends...sometimes in life I do believe that you have to get away from ppl that might not be good for you. However in your case it sounds like the person you need to get away from is the ex girlfriend.
Stay positive....and let me tell you it is much harder to do then to say. Before you go to bed each night...talk about your situation....I am not saying pray...but talk to a higher power. Sounds stupid but actually talking about it seems to make you more clear in regards to what is going on. When you talk about it...be honest (no one is there to hear you). And when you talk about it...try to make yourself speak positive.
Try to find a counsler....trust me I use to think this was a bunch of crap....however...it does help if you find the right one. And don't be worried to change if you don't like the one you have. There are a few out there that are pretty koo koo ca choo....so if you don't mesh with one...get another. If you don't have the money....there are counseling agencies that work with you. Look at it this way....it CANNOT hurt.
In regards to medication....you do not have to have a chemical imbalance. Through life sometimes there are times that we as humans have a hard time dealing with. Doesn't make us chemically imbalanced...just makes us human. As we mature our bodies change and sometimes it is harder to rebound from things. Now trust me on this...I am 43 yrs old...and use to think ppl taking meds were ridiculous....just snap the heck out of it. Well then came my issue....mind you I am a pretty typical girl...I have a great husband a great son, a great house...etc. I thought I was having a heat attack...mind you...I was in great shape too. This started happening 3 years ago when my hubby went to Iraq. You COULD NOT convince me that this was a mental thing. It took them 3 years and dozens of specialist and tests to finally convince me it was not a physical thing. It was anxiety. Well....I am now 6 months into taking a pill for this. No chemical imbalance....just anxiety. I still sometimes go back to ...no way this is the problem. But I have to admitt since taking the pill each day I have had no more....Oh my god I am having a heart attack. The reason for this story is to show you....even the most balanced ppl need some help sometime. Its ok...we are human and NOT perfect. We just sometimes need help. Depression can cause all kinds of other problems as well if not handled. I pretty much blew up my digestive system due to the anxiety. Don't let that happen to you...deal with your situation and you will be smarter and better in the future.
Ok...hope this helps you put some stuff in perspective. Take responsiblity for your depression...remember only you can control your emotions.