Keep in mind that your girlfriend is, as you say, over 10 years older that you. She's had a lot more time to get herself together than you. It doesn't happen overnight. You will get there eventually. In fact I'm sure she's probably been in the same situation you are in now when she was your age. That's likely why she is so supportive of you and is willing to wait. She probably understands and appreciates what you are going through. Don't be so hard on yourself and yes one step at a time.

Think of depression as any other illness. I was depressed for over 40 years. I finally found my way through by exercise and meditation. Especially meditation. Your body reacts to every thought you have. Meditation helps you realize that you will always have uncontrolled thoughts. It will also help you realize that most of those thoughts are bullsh*t. You don't have to react to every thought you have - especially the negative ones. Just laugh at the silly ones. And speaking of laughter, fill your life with crazy laughter. Go to the comedy clubs as often as possible. They are not expensive. And exercise will help you fill better physically, which will help you feel better mentally. And exercise, meditation, and laughter will all help you get more oxygen into your system. And oxygen is the lifeblood that heals your body and mind. Mainly, just live your life as if you weren't depressed, and then one morning you will wake and you won't be depressed. I remember one of the most depressing things I had to face every day was the fact that I was depressed. But then I quit thinking about it and I just lived. And then I was just someone who was having a bad day. Everybody has a bad day every once in a while. So you see, you aren't so bad off. Doctors like to say that depression is caused by a chemical imbalance in the brain. I'm not so sure that the chemical imbalance in the brain isn't caused by depression. And depression is caused by way too much negative thinking and believing those negative thoughts have real consequences. You may not get to choose what you think, but you do get to choose how much validity you give to those thoughts. I highly recommend Victor Frankel's book "Man's Search for Meaning". One concept he puts forth is that we have a thought (consciously or unconsciously), but then there is a moment where we either choose to believe that thought, act on that thought, or discard that thought. YOU HAVE THE POWER!! Meditation will help you find that moment where you deal with your thoughts AS YOU CHOOSE.

Get yourself a shot of underground testosterone. You do not have depression at all. The doctors always misdiagnose Low T.

I hear you. I see you. I empathize with you. The help i can offer is only advice, please use what works as it aplies to you. Dont try to put all your troubles on your relationship, instead call on safe(caring & understanding) friends & family. cousellors can be a great help, spread the load, ask for support. Your girl friend will be there & you can have the future you both want, just deal with you one day at a time. ask her to take the pressure off while you heal,let her know you want the same things (hopefully you do) she does.
meditation & exercise(as mentioned by 123) will help more so than medication in the long run, but meds have their place in the beggining. Diet & sleep are key, creative outlets can help alot. Your not alone, many suffer with the same feelings especially these days. Focus on being greatful for the little things (stupid stuff like-animals,kids),anything that puts a smile on your face & makes you laugh-share it with whoever is around. Let your girl know often the small happiness you discover. remember to laugh with her as much as possible, make it a priority.
Carry with you these words, "You may only be one person to the world, but to one person you mean the world." Thank you for your courage & strength to share your burden, it lets the others know the're not alone. You made my day. Peace & Blessings.

You're taking the right steps. Depression is an incredibly hard disease to beat because you do feel that way - that you're a burden to others. Now that it's diagnosed you can start to find out what alleviates some of your symptoms.

First things first, know that your girlfriend is just as lucky to have you as you are to have her. You have each other. Work at beating the depression for you. You will find your way out of this and your relationship will be much stronger for it. The good thing about knowing what you're feeling is depression is that you will recognize the signs later in life too and be able to take steps to nip it in the bud.

Much love to you both. Keep on recognizing what you're feeling and addressing it. That's half the battle.

Seconding the recommendation about exercise and meditation. Feeling Good is a great book that's helped me many times.

....underground testosterone? who knows what the hell is in that shot?? and also, while it is true that some men may have depression due to very low testosterone , here are a few things to consider: your family doctor first has to send you to an endrocrinologist, then that specialist has to run tests to truly determine if you are very low on T. the testosterone comes in gel patches, gel cream and injections and they are fairly expensive. It is something that once you start, you have to keep going back to your family doctor for the biweekly testosterone. Also, your body itself will recognize it is getting external testosterone (from injections, gels etc) and the body will stop naturally making its own testosterone....so once you start, you have to keep getting biweekly injections/gel/patches for the rest of your life. There is much more info...google it and educate yourselves.

(well, except for testosterone..) are so wise, thoughtful and caring. I'm not the OP but it was really nice to read all of them. There are some good people out there. btw, totally agree with the exercise and meditation.