Hi,
have you considered seeing a doctor about the way you feel? They can give you anti-depressant medication which they think will most likely suit you (depending on age, type of depression etc).
It can be hard talking about your feelings especially to someone you don't know. If you find it hard just keep posting on here, it might help you alittle. Do you do anything like writing, or drawing - that might help express your feelings too.
I can imagine that it must me very stressful, that you are in a relationship with someone who also suffers from depression. Do you have any other stresses in your life like school stress or family problems or anything? Sometimes depression can also be caused by poor diet etc, do you feel that you eat well. You could also maybe ask your gp if they can test you for illnesses such as anaemia or diabetes - these illnesses are often related to depression.
Hope this helps you alittle.
Take good care.