Think of it this way: if you don't say anything to them, they'll just assume you're good with whatever. 

Regardless what it is, be it something that's happening in a roleplay, plot direction, or your own mental health, if you don't communicate with whomever you're writing with (group or otherwise), there's no way for them to know what you want to do. So yes, the best thing to do is be honest about where your head is at. If they aren't going anywhere and are plenty invested in the story you guys have, they'll wait as long as you need to regroup. And if they're not, then better to end the writing partnership before it gets too toxic.