1. Writing is not mysterious to them, so they will not romanticize, mythologize, or idealize what you do.
2. You will not as easily be able to get out of things because you need to write. (And you should be able to. You should be able say “I can’t go to the movie tonight like I said I would, because I got this idea and I have to write it down, otherwise I’ll lose momentum.” It’s a legitimate excuse.Paradoxically, non-writers are much more understanding about these things than writers.)
3. Reading and/or critiquing each other’s work is terribly awkward and fraught with nuance. It may result in the laying of emotional landmines.
4. If you are more successful than they are, they will, at least on some level, be jealous. If they are more successful than you, you will, at least on some level, be jealous.
6. One person using the relationship as material is problematic enough. Both people using it is like CatDog trying to eat itself.
7. You will be poor.
If not other writers, though, then who? Readers, of course.