@braincheese
Hi there,
I'm sorry to hear that you've been going through depression for so long. Depression can be realy tough to deal with, and one of the hardest things can be telling family and friends.
When it comes to telling them, the first important thing to remember is that it's up to you if and when you tell people. Telling people can take a lot of courage and it's important that you only tell people when you feel ready. You mentioned in your post that you've had depression for ten years and kept it hidden, so the fact that you're asking this question now suggests that you feel ready, which is really good, but if it comes down to it and you get too nervous, it's perfectly fine to wait a bit longer until you know for certain that you're ready to share.
The second important thing is to remember that people have faults. When you share this kind of news with somebody, it can be hard for them to take on board. Of course, you'd hope that they would respond positively and supportively, but it is important to know that unfortunately this might not be the case. People can respond badly to this for many reasons, for example (like you mentioned about your mum in your post), they might not understand mental illness properly, or might believe that it's not a 'proper' illness. Of course, you and I both know that this is completely untrue, and that depression is a very real and debilitating illness, but unfortunately, not everyone knows this for themselves. Another reason for a negative response is that the person might feel bad or guilty that you didn't feel able to tell them sooner. It's important to remember that however they respond is their problem, not yours, and that if they are unsupportive, there are plenty of other people who are willing to support you and listen to you and you mustn't feel guilty about how the person reacted.
When it comes to actually telling them, I'd recommend doing whatever works for you. A good way can be to sit down with them in a relaxed and calm environment, and to do your best to explain it (it can help to write down and practise what you're going to say before you do this). If this is too hard for you, other ways could include writing it down in a letter and giving it to the other person. Talking is usually the best option, but this can be extremely difficult, so sometimes a letter can serve as a way to start a conversation. Afterwards, you may need to answer questions from the other person which can be tough, but is something tht you can prepare for.
After you tell someone, you may also want to let out how you're feeling. To do this, you can talk to anyone: a friend who already knows about your depression, a 7 Cups listener, or even just writing your feelings down in a mood journal might help. You can also speak to a 7 Cups listener if you require support before, during, or after.
I hope some of that helps and that everything goes well!