>>251294
I co-wrote a long one with my ex about a girl pretending to be a boy so she could be a squire and the evil knight who was assigned to train her. It ended up actually being novel length.
Writing smut is not like ERP. With ERP you get frequent feedback and half of the writing will be your partner giving you tons of content and ideas. There's always new stuff coming your way with ERP. Writing solo means that you have to have all the ideas and all the steam yourself.
Co-writing, which I did some of the time, is closer to ERP but still not quite the same because we would plan scenes out again of time very meticulously before writing together in a google doc. I don't recommend it instead of ERPing unless you have someone you work very well with.