Ivan,
See someone about it, and get professional and capable assistance.
If all that you do is to find someone that you can have a massive whinge to, then do that. Hanging out with other people that are calm or upbeat is great.... being alone is not so good.
The trouble with depression is that its easy to keep going down .... it can lead you to places that you don't need to be, and that you might not need to get to if you seek a bit of help.
Depression and sadness are real, normal and reasonable emotions and we all have them. They are the result of brain chemistry affecting moods, but the trouble is that the moods can affect the brain chemistry in return.
The good thing is that when you come out the other side you will be a better person for it, and will be more resiliant to life's knocks.
There really is no substitute for seeking assistance.