Hello wizardy: Welcome to PsychCentral... from the Skeezyks!

I hope you find the time you spend here to be of benefit.
You know... I am where you are a lot of the time. What your brain is telling you is depression talking. And depression can be treated. Personally, I think it would be fine to share how you feel with your girlfriend. But I also think you may well be correct. It may not change anything to a significant degree. What you need is therapy. And if that isn't sufficient, then perhaps antidepressants. (Assuming that these things are available to you where you live.) You mentioned that you attempted suicide once before. Statistically, this makes it more likely that you may try again. (I've done so.) It's important to acknowledge you're ill & to reach out, in real life, for the help you need. But also keep posting here on PC. It can help too!
It is true, I believe, that when one person who struggles with depression becomes involved with someone else who also struggles with depression, the whole situation becomes more complicated. On the other hand, the "up-side" of this is that you can understand & hopefully support one another. It's just important that you both acknowledge your individual struggles & commit to doing what is necessary to succeed as a couple. From what you wrote, it sounds to me as though you & your girlfriend are lucky to have each other. This is a rare gift. Please don't throw it away! I don't know what it was that caused you to attempt suicide to begin with. But you're young, you apparently have a good job, & a wonderful budding relationship. That's a lot to live for & to be celebrated!
I send healing thoughts your way with the hope that you will be able to find the strength to overcome...