The only thing worse than going through depression is being in a relationship with someone who is showing signs of relationship depression. It is difficult to watch them go through this dark period of life. Many relationships end because of it because there doesn't seem to be any end to it and it begins to wear on both people in the relationship.
Depression makes people think irrationally and causes them to be blind to the good things in life, like you. They will make you feel like everything you do to try and make their world a little better is a wasted effort. It isn't, though.
The fact that you are there beside them means more to them than you will ever realize. They wouldn't blame you for leaving and will sometimes try and make the decision easier for you. They don't really want you to leave, though. They want you to be with them and help if you can.
The first thing that you can do to help them deal with their depression is to understand it. Educate yourself about this mental disorder. Seek out to find what causes it. It could be because they lost a job or did something that brought on a feeling of failure. There are many reasons that it could have started but one thing is certain, even if you are in a strong relationship, depression, once it has begun can snowball.
You will need to make sure that you take care of yourself in this relationship. Depression, gone unchecked, can be contagious. When you are learning about depression make sure that you are watching for signs that you may be exhibiting. If you are then you should be quick in seeking help from psychologists or counselors. Once both of you start falling into depression it may be impossible for either of you to see the light of day. When you start getting worn down because of the weight of it all try and take some time to step back away from it and take care
A past relationship and depression sometimes go hand in hand. When a relationship has failed it is easy to feel like every relationship after that is doomed to fail. Once someone begins feeling that way they will many times turn their current relationships in to a failed one. If this has begun to happen it is important to get relationship advice from marriage counselors and work with them to prevent it. This is not the only reason that marriages or dating relationships fail while one is in depression. Just the strain will cause it to suffer. Seek relationship advice from trained professionals as much as possible.
Above all, do not give up. Believe that you can help them overcome their depression and believe that the effort you are making matters. There are few things more powerful than what can come from a strong relationship. Depression is a tough foe but it can be beaten when the one you love has you to depend on. With a strong relationship depression can be beat.