This is something important for you to know, because it will make you feel better and because whenever somebody is depressed, we worry about them doing irrational things. There's one thing that's amazingly simple but it works. When you're very upset, breathe *slowly* and *deeply* until you've calmed down. An expert recommends breathing in through the nose - 4 seconds, then out through the nose, 6 seconds. There are other things you can do when you're at wits end. Within reason, a little extra food helps, although binge eating doesn't help and especially not alcohol. Distractions - a funny movie, music. Any music that makes you feel better is good. Many people say a brisk walk around the block can do wonders, especially on a sunny day. The weather is getting great, and you'll love time outside.
What I'd caution you most about now is getting agitated. The suicidal feeling is a panicky feeling that you must act quickly, so the thing is to slow down and get calm. Don't let that feeling hustle you. You've got all the time in the world to work your problem out.
It may be that your friends and your girlfriend would work night and day to help you. The thing is, they're not mental health professionals, and that's what you should have right now.
Friends can help depressed people by having fun with them out in the fresh air and sunlight, getting exercise with them. Taking your mind off your problems, even for a little while, is therapeutic. That's some of the depression info you can read about in my answers. Feel free to click on my name and read.
DBT -coping in a moment of crisis
https://www.youtube.com/watch?v=MXxatFoSbeY