A few additions
Firstly, here’s an international list of support agencies collated by @zephyr1 quite recently
My personal tip is this superb yet accessible book
This particularly resonates and des with this kind of feeling
As someone who has dealt with a number of suicides and dozens of attempts, my simple advice would be to be aware of changes in the volume of conversation coming from players who are normally chatty. People who are feeling low often drop off the radar and sometimes a friendly ‘are you ok?’ is invaluable.