For me, I hate when players drop due to lack of interest. (In a 1x1 sense, as groups are a different ballpark...)

If someone isn't interested anymore or is bored, I would think they would speak up and help fix their problem, rather than walk away from it entirely. In a one on one, two people are communicating to ensure they're both enjoying a story they make together. If one is unhappy, the signs aren't hard to miss and yet it always goes beyond the point of fixing a stale point or plot. The bored player doesn't speak up until they've given up and the other player is already resigned, possibly expecting their partner to drop. So why can't someone speak up and be proactive rather than passive? I understand that sometimes the content itself (the setting for example) is getting dull but if the plot and roles need to change, that shouldn't be a difficult thing to do. So many people in one on ones walk away from their partner without trying to fix it or at least have some closure. 

I think both parties are at fault.

But the more criminal one in my eye, is the one who walks away without an attempt to fix it or start something else.

So when partners leave, I feel like my time has been wasted, as has my outreach to befriend them. Sure, some RPs can be called off on nicer terms but usually, I invest myself into a RP. When it's ended prematurely and without a good enough fight to keep it going, it pisses me off. People will lose interest in things though, it happens. What pisses me off is when they give up and don't try to make things work. No, I'm not advocating that RPs should be forced to continue if the writers aren't happy. I just think writers should be more considerate of those they end up ditching without trying to mend it. After all, if they're bored, they are ultimately the ones who need to figure out how to stay interested or to change something to make them care again.