It is hard to live with someone who has depression. I know because I've done it. With several family members.
I also know it's hard to live with someone who has depression, because I do see how it affects my family when I'm "off."
It is particularly hard when the person who has the problems is not aware of how bad they are or how much they affect everyone else. If someone is not self-aware, is too self-centred (which sounds like the opposite, but is not), and is just not aware of how they affect other people, it can be almost impossible to live with them. And you want to be sympathetic, you want to be caring, you want to help, but the person you love is being hard on you and your other loved ones. It's a bitch, really.
Substance abuse, emotional abuse, physical abuse, any kind of addiction, can all be direct results of depression, emotional disorders, and mental illness.
So how do you deal with it all?
I'm not an expert - but I have some experience. And my first advice would be for you to go to the doctor with your loved one and read as much as you can to get a good understanding of what the illness is, how it affects the person's brain and what behaviours you can expect. Andrew Solomon's "The Noonday Demon" is a good place to start, but there is a ton of information out there.
The rest that is following is only based on my personal experience, and it will not be the same for everyone. This is not to be confused with medical advice - these are not guidelines to follow, but you may see something here that makes sense to you.
If I am in in the throws of a depressive/anxious episode (and I'm not talking about being locked in my room crying for days on end - if someone is that bad they may well need to be hospitalized - and don't be afraid to do it, it could help more than you know), but I'm talking about when I'm being irrational and over-reacting, I need for my husband to not take anything I say to heart. I'm lashing out. And I really don't mean to.
Here's what happens - I feel like crap - I'm not necessarily aware that it's my brain chemicals causing my feelings, so I try to figure out why I'm feeling so bad. My thoughts go towards the people I spend the most time with - because it would most likely be them that would cause me to feel bad - and I try to tell them not to do that to me anymore. Problem is that it wasn't them who caused me to feel bad. It was my brain chemistry. So my husband needs to take EVERYTHING I say at these times with a grain of salt and talk to me the next morning when I will likely be feeling better. But not everyone will feel better the next morning.
I really have had to try to learn not to take it out on my loved ones - and I'm still not perfect on this front. At the ver least I try to realize that I am doing it. It really helps to have an understanding and dedicated partner. I don't think a weak relationship could ever survive this crap. And although I am feeling bad, I still have control over my actions. I need to be aware of them and their effect on other people.
It also helps to have a strong support network - for the ill person and for their families - friends who have gone through similar things. It helps.
Medication is not the enemy. No one out there on antidepressants WANTS to be on them. Every single person wants to get off of them. So if you need them and you don't want to need them, well, you are like everyone else. But medication can be a life saver (literally) and a relationship saver (literally).
If I don't feel good, sometimes getting out of the house is a good thing. It can take my mind off of how I am feeling and can help to break the spiral cycle. Or it can make it worse if I have interactions with people that aren't positive. And alone time can be necessary, too. I really depends. I can't give you any advice on that one.
This is all fluid and changing - and the brain - thoughts - change quickly. I can be feeling like irrational shit minute and feeling fine the next. Then back to shit 5 minutes later.
You need to communicate and understand that it is not your fault that your loved one is lashing out. It's not theirs, either. It's a brain chemistry imbalance and you all need to learn to deal with it.
And it's hard, by the way. But it's worth it. Your loved one is still there. They are still the same person, and they can become balanced again. It takes time and action.