You've met somebody, and they're great. You're all up in each other's business, everything is going perfectly, and then, they reveal they have a serious depressive disorder. What to do? Well, the first thing to know is that you won't be on your own in figuring out how to best support them: there is a lot of scientific research out there about what precisely to do to help a partner struggling with depression. Whether it's guidance regarding how to react to rejection when they're in a depressive phase, how to best express emotional openness, or whether or not to go away for a long weekend and leave them in a funk in their apartment, science has advice.
Before we even get into the specifics of scientific advice, though, the best thing you can do to start is research depression yourself; you can also get to know how your partner's depression works and how it's managed. Partners are often useful back-ups when it comes to self-care — you can encourage structures that help your partner manage their symptoms, including getting them to take their medication, wash, get out of bed and eat properly, which is a good place to start. But you've got to do it in a way that's sustainable, doesn't make you their parent, and lets them help you in turn when you have an issue. It can be a tricky balance to strike, but luckily, there's a bit of expert advice out there to help you.