I've noticed something: I can't write when I'm in a real relationship. I was with Alex for three years. I probably wrote less than 100k in all that time combined. I understood that it would be hard to write at first -- within that "honeymoon period" (I hate that phrase), it's reasonable to expect that some hobbies will fall through the cracks. But everyone said it would get better; it would get easier; I would return to my routines. I never expected that I was making a solid, long-term trade.
It didn't get better. It didn't get easier. But a month after we broke up, I wrote 30k in around a week, and it was all GOOD. 30k keepable, staying-in-the-draft words is probably as much as I wrote in the whole three years we were together.
I can't really offer advice, but I can certainly confirm the phenomenon.
It's similar to how I am with hobbies, except to a vastly greater extreme. I usually go through cycles with my hobbies. I'll knit obsessively for a month, then throw my knitting needles in a box for half a year. I'll read five or six books in the course of a few days, voraciously devouring the text... and then not buy another book for a month or two. I'm used to engaging the world like that. But with a relationship, it's different.
A major part of the reason I write is a combination of two factors:
1) I am a complete control freak, and
2) I crave social interaction but have difficulty finding people I want to interact with.
When those two needs are both unsatisfied, writing steps in to fill the gap. I can create a "social life" by emotionally engaging with the characters. It gives me someone to care about in a completely safe, totally predictable kind of way. I don't always know what my characters are going to do, and I don't always know who they're going to become, but ultimately, I can just press the "close window" button at the top of my screen and never touch the document again if I feel like things aren't going the way I want to. I can abandon them and reclaim them at will. I can choose how much I want to empathize with them, and I can manipulate my own emotions by manipulating my characters. Writing gives my control-freak side something productive to chew on.
When I'm in a relationship, I don't have those needs. When I'm in a relationship, one of two things happens to my control freak tendencies. Ideally, they're significantly diminished. I get much less panicky and I'm capable of being less uptight, even capricious or impulsive sometimes. Worst case scenario, I'm too busy trying to use my control-freak tendencies to force a doomed relationship to work -- there's no time for me to play around with writing when I'm trying to defibrillate a flat-lining romance. And obviously having a partner fulfills my need for social interaction within the relatively narrow classification of people that I actively choose to interact with.
Sometimes I convince myself that I'd be happiest if I spent the rest of my life alone. I enjoy relationships. I love the depth and the personal expansion and the connectedness and the things I can learn. But when I start to question it, when I ask myself which I'd rather have written on my gravestone, "beloved of ____" or "beloved author," I start to feel uncomfortable. I've had two life-changing romances, lasting nearly three years each. I've had my time to love people and to be loved in return. And I start to convince myself that maybe I've gotten my fill of society for a while; maybe I should invest my emotions in a page instead of a person.
I don't think I could possibly love a human as much as I love writing. Even having two people I would die for, in a literal, logical and non-exaggerated way, even THEN I think I'd rather have a life of books than people. And that scares me a little bit.