I think one of the main problems for me with this kind of thing is what a lot of 1x1 partners are like. When you've been forced to drop another RP, or had another partner just disappear it gets hard to be positive and have any interest in any RP. I'd usually just leave for an amount of time myself if I didn't have any RP going. I tend to forget the bad parts about it after a while. It's one of the reasons I think I want to try GMing at times too. I forget how awful it really is after a few months.

At the moment I have one RP that I've done for like 9 months, and it's had its ups and down. There were times I didn't feel like posting at all, but I just forced myself to do it in the end. I think the main interest still remained thanks to good character chemistry and probably the best 1x1 partner I've had. There was a story planned out for it at first, but once we passed that we let the characters lead it where it would go and that made it more interesting cause you didn't really know yourself where it was going. We've tried to change it up quite a bit too over time.

I think for a group RP it needs to have something that I can't get in a 1x1, but again the other roleplayers can be what makes me lose interest and not want to do it.