The thing about love and depression is that they share an awful kinship. Both are insidious and consuming and tend to make you drink more than you should. Both steal your sleep from you and mess up your working life, and both make you feel like nobody else could possibly have ever felt this way before, ever.
The difference is of course that falling in love is ostensibly made of good feelings and being depressed is made of bad, a whole bundle full of bad. To a depressed person, falling in love is totally terrifying. When you're tormented by the depression gremlins, it's hard to trust any good feeling and even harder to not spend most of the time worrying about how and when it will go away.
It's also difficult when you're beyond blue to understand why this excellent human would want to tangle themselves up with your melancholic little heart. Most depressed people aren't depressed all the time and rarely impose their depression on other people. They aren't mopey Eeyores bringing down everybody's honey party. No way. They're usually total Tiggers! Nobody compliments others or makes hilarious, self-deprecating jokes like a depressed person! (Then they drink too much, go home with someone they don't even really like, pretend to be asleep until the hook-up leaves, and hide under the covers for a week watching East Bound & Down with their phone on silent.)
So in this way, the cerebrally unpredictable can be very charming and lovable and people often do like them and want to be close to them. There are even some sickos who cultivate an air of depression to attract other people. To the honestly depressed this seems as horrible as non-alcoholic beer at a barbecue but, it happens. Dudes who fancy themselves as young Hunter S. Thompsons or Bukowskis, and girls who actually think it would be glamorous to be Sylvia Plath or a tedious Kirsten Dunst circa Crazy/Beautiful - or any other of the billion awful pop culture appropriations of depression – these people confuse selfishness with depth and put it on like a winter coat.
If you're depressed and you fall in love it's like someone throwing you an inner-tube when you're drowning. Maybe you're not the worst person in the world! Maybe this will pull you from the gaping maw of loneliness and self-doubt! Maybe this relationship is exactly the mortar you needed to fill all of the cracks in you! Maybe, just maybe, this new love feeling will stick around forever or even if it doesn't maybe you can hide your depression gremlin for long enough to lure them all the way in with your Tigger jumps until you've got them caught and then they will be trapped in your dungeon of love forever! Ha ha!
Sorry, no. Because after the first stage of love comes the part where you have to actually open yourself with a zip, right down the front of you and let the other person see all the gross bits inside. And do you know what you're going to do to this person if you don't deal with your depression outside of the relationship? Oh man, you're going to make them miserable. You will challenge their feelings about you because deep down (or even not so deep down) you have such a low opinion of yourself, you're suspicious of their feelings. You won't be able to see that it is totally not fair because they aren't even your feelings. Sure, they're someone's feelings about you, but you don't own them! Knowing that won't stop the gremlins though, they will still pick away at you from the inside. Not only will they make you challenge your sweetheart's view of you, the depression gremlins will point out the value in every other person your person-of-interest might like and make you lousy with jealousy. Because you think everyone else is better.
The other side of the same coin, when you're the one falling in love with someone who's depressed, is just as tricky. In the way that being loved won't fix you, falling in love with a depressed person won't fix them either. You will never be able to reassure them of their value or your feelings enough. They will retreat to places your cheerful ideas, thoughtful suggestions and offers of sex and bakery treats can't reach. If there's two of you? Then you're basically that couple in Open Water, treading H2O and waiting for the sharks to come.
Love won't conquer all - but it's a damn good reason to get help. Because the other things love and depression have in common is that they're very real and big and there are excellent ways to manage them both. Just because you're depressed doesn't mean you don't deserve love or that you can't be excellent at it. Counselling with a professional, a little bit of patience, and maybe a few pills here and there for a while, and before you know it you'll be having dinner parties and making everyone else really uncomfortable with your disgusting nicknames for each other, just like a "normal" person.