On my way out the door, a handful of quick thoughts:
1. Most importantly, you're not a broken person. This is the sort of thinking about mental problems that has to stop. If somebody had the flu, you wouldn't refer to them as "broken". Being depressed, even suicidal, shouldn't be a factor in how employable you are. At the moment, you're not making full use of your talents, but that happens to everyone sometimes.
2. You've recently had some major disruption in your life, and it sounds like you don't have anyone to talk to about it. You refer to your girlfriend as your identity; that can make the end of the relationship especially brutal. This is why it's so important to have a sense of self, an identity all your own, before getting into a serious relationship.
3. Most people are not equipped to deal with someone who's depressed or suicidal, or even having an anxiety attack or any number of other mental illnesses. Don't let your experience with your ex-colleague make you give up on talking to people. Talk to people about it. Use your best judgement.
4. This is why therapists exist. They are trained to have conversations like this and to help you sort things out. However, finding a therapist is a lot like finding a romantic partner -- it can be discouraging and it can take a lot of work before you find someone that's compatible.
5. Depression (and other mental illnesses) and problems with sleep seem to be correlated. And, the middle of the night, when everything's quiet and your mind is racing and there's nobody to talk to is a bad time for people with depression. So, put some serious effort into getting good sleep for a while -- even if it means going to the market and picking up some over-the-counter sleep aids. Go to bed early, pass out, if at all possible sleep in without an alarm.
6. DO THINGS. Depression can spiral out of control when you're locked away in your home, or just making quick errand runs. I can't say whether or not you should quit your job. Maybe the job isn't what you should be doing right now; maybe it is exactly what you need to be doing right now. I dunno. But, you need to be going out and doing things. New things are great things to do. If you have some savings, now might be a good time to spend some of it. It's your rainy day fund, and it's raining right now. You're worth spending money on. Go somewhere you've wanted to go. Try something new. Get on meetup and float through some new groups. Re-connect with old friends or family you haven't talked to in a while. You never know when something that you experience might change the way you feel about yourself and the world around you.
7. Depression, in my completely unprofessional opinion, is primarily a fault with the way a person perceives themselves and the world around them. It's like a form of mental blindness: everything sucks, I suck, I'm a bad person, I'm worthless, the world would be better off without me, life is too hard, etc. These things are all wrong. If you can alter the way you see yourself and the way you see the world around you, your depression will improve. But it's hard to do that by sitting in front of your computer.
8. You sound young. I don't mean that to sound dismissive; rather, there's a lot more life ahead of you, and you'll be missing out on it. You've got at least another 10 years to meet someone great and raise that family you want; 10 years is a long time. (At least until you get to around 50 or so, then 10 years seems to go by pretty quick.) You have no idea who you might meet or what will happen in the next 10 years.
9. Don't worry too much about your reputation. For breaking news: just say, "I've been struggling with some pretty severe depression recently. I'm working on it." Really straightforward, matter-of-fact. Nothing to be ashamed of. Having frank conversations about it is a heck of a lot better than waking up dead one day.
Your post got a pile of comments. People you've never met before care enough to try to reach out to you. That's a good start. Go from there.