A question I always ask myself is what would I advise a friend to do in the situation? Strange how often the solution presents itself.
The sooner you have the conversation, the sooner you will be on the path to recovery. It isn't just the help a GP can offer, it is vocalising how you are feeling, asking for help and taking the first step that is important. You recognise that talking is important for your friends, you deserve a sympathetic ear too.
Mental Health is the most common reason people see their GP. They hear about suicidal thoughts all the time, I was worried I'd be locked up or something when I spoke to my Dr but that really doesn't happen, millions would need to be admitted in that scenario.
You may be surprised at the range of people who have mental health issues, including many seemingly together people with well organised lives, loving families, good job, etc. Your Dr won't be surprised when you talk, they've seen it before.
I recommend writing down what you want to say before you go and reading from that in the surgery. If you struggle to get it out, give the paper to your Dr to read. Your Dr will be interested in symptoms, how do you feel? How does what you feel impact on your life? Any immediate plans to jump in front of that train, Etc.
First port of call for your Dr is usually pills. Nowt wrong with that, they have helped me enormously but I would seriously consider asking to be put on the waiting list for counseling too. To my mind, if you are ill enough for pills then you are ill enough to benefit from counseling.
Hope that helps.