Not in the U.K., hence no COVID restrictions:
I was selected to be involved with a project (non work related). I had to interview for it and was successful so am now part of the team working on a particularly thing. It is dependent on all participants being available in order to go ahead.
I have an extremely busy life. I'm a single parent and when I'm not with my kids, am juggling long work hours, two other projects and a busy social life.
I checked the required time commitment before I signed up and it sounded doable.
We set our schedule (about 5 days over the span of a month) and I planned my life accordingly and all was good.
The problem is that lots of additional days keep being requested and I'm proving quite unpopular with them because I plan my schedule a few weeks in advance because of all the things I'm juggling, plus coordinating with my ex. Ex is usually flexible on our custody schedule but I can't extensively mess him around. Everyone else's schedule on the project is much easier than mine and the other team members are getting disgruntled.
Due to unforeseen (genuine) circumstances, they now also need to move something significant and it'll now take up two full days where I already had plans, some social (when kids at their dads), some with my kids. Changing everything would be a nightmare, piss off my ex and my friends and lead to missing quality time with my kids. It is actually an unavoidable change that they didn't foresee but nonetheless I am struggling to coordinate around it.
I'm trying to to balance being cooperative and a good team-player with drawing a line that it is something I'm doing voluntarily (albeit a fantastic opportunity).
I feel terrible but equally people around me are getting really annoyed at all my last minute cancellations and schedule changes to accommodate the project.
Then project leads have now requested that i 'try to just keep your schedule totally clear till the project is done', which seems insurmountable to me, and I'm just super stressed out with it now.