So I'm saying IF your ADC refuses to cooperate, if it's hopeless, etc. then just leave. Obviously if your ADC is cooperative and your immediate presence there is beneficial then roaming would be ill advised. This is because roaming creates the potential for plays, the map pressure, as opposed to a guarantee for a play. But if enemy bot lane is exerting pressure in such a way that a 1v2 vs. a 2v2 difference is large, then why not stay where you are guaranteed to be useful.
So this sets up my previous statement which is that when the bot lane is missing and you are playing an aggressive support champion such as Leona, Alistar, or Blitzcrank, you should be roaming to mid or enemy jungle (with your jungler for example) to make plays there rather than sitting in a bush in your lane waiting for nothing to happen. Similarly if your presence with an uncooperative ADC who is upset by your mere presence and refuses to perform, then you might as well leave. It's going to be a 1v2 either way.
in the case of a support just sitting in a bush doing almost nothing, then yeah I kinda see what you mean. that'd just also mean they're a bad support too.
That slump has happened to me before too, best advice is to just take a 1-2 day break. It usually happens if you play too much of something haha