Besides antidepressants? There’s very few things I’ve found that helped bring me out of that funk. Going out with friends did help a little, although I live pretty much alone so it might be different for someone who is living with an SO. Walks can get the creative juices flowing, as can just general exercise like pushups in your living room. The only solutions that aren’t clinical are going to be soft-fixes though, and a lot of times the only way to power through the anhedonia/depression stopping creative acts is to just force yourself into writing a bunch. I found that sometimes when I really pushed myself, I’d go into somewhat of a writing fugue where everything else just seemed to disappear.
Some other techniques that might help are setting a deadline for yourself, although this can increase anxiety. Setting small goals and working through them in chunks can help as well as it lets you feel accomplished for each step rather than focusing on the end goal. Setting daily challenges like “write 1000 words” or “write 500 more words every day for a week” can make it seem more like a game, which has definitely helped some people although I could never get it right.
Working through mental illness is tough because of how unique everyone is. You have to find what works for you, so continuously try new things. Even if they don’t click right away, give it a few days to weeks. Most importantly, there’s nothing wrong with needing to take a day or two of rest as long as you get back on that horse eventually.