Hi flobadob. You are not alone! Clinical depression is very common. I have it and have been deeply suicidal at times. I hate pills, but know that when I am going downhill it's the only way to deal with it. It took my GP a long time to convince me, and I now know that she is right.
In a way, you are lucky because you recognise that you are depressed; many people are afraid to consider that as a possibility and it is very difficult to treat them.
Don't be afraid to get help from your GP, and don't worry that you might end up on pills for the rest of your life; it doesn't have to be like that. If you are suffering from a physical imbalance of chemicals in your brain, then this has to be addressed in order to get better.
If you also need to just talk to someone, the Samaritans are excellent - they are there to listen, NOT to give advice, so you can just offload as much as you need to, as often as you need to, and for as long as you need to. Give them a call and try them out, but don't expect to get urgings to go to the GP, etc. - they will regard that as not their place - they are their to LISTEN to you, not to push you off onto other people.
Please take your condition seriously and get it dealt with professionally. Struggling on alone is not the way to do it, although I understand your not wanting other people to know the nature of your condition; but anything you tell your doctor is confidential, and there is no reason why anyone else should know if you don't want them to.
What about your fiancee? If she knows about it then she can help to support you through it; if she doesn't know, then she won't understand any strange moods you may suffer from, etc., so it might really help the both of you if you can share it with her.
Take care, and please take the necessary steps to get treatment. Please come back and let us know how you are getting on; I, for one,