Well done for calling the Samaritans, and being honest with them. I hope you do remember to talk to them when you need that extra support.
WRT volunteering, I’ve worked for CAB and for a signposting service at my local hospital. Obviously, I also help out here. I know that, in those environments, you may have to deal with all sorts of things that can be very triggering and have had to step back countless times to protect my own mental health. Please, please, please consider very carefully whether it’s the right thing to do at the moment. That’s not to say you might not do it in the future, but maybe when you’re more settled?