It sounds like you have compassion fatigue, definitely.

I think you also need to realise that it's not your job to help everyone. You need time to recharge too. Setting boundaries is not selfishness.

It's not your job to look after a friend's child, even if that friend has brain cancer (especially if you haven't seen that friend for 10 years). Even if that choice to help them would be an altruistic and noble choice. Just because you COULD do it, and doing it would be a good thing, doesn't mean if you don't do it you are a bad person. You have only a limited time every day. You should focus on healing and recovering from depression, and once you have your energy back (and it will come back) you will be able to help people in better ways.

Long term, looking after yourself now will allow you to help more people in the future. <3

Also re Facebook - I used to be addicted to Facebook as well. It's literally an addictive software that is designed to make you mindlessly scroll. I have deactivated it and only use messenger now. But don't feel bad for being sucked into a software designed to suck billions of people into it and make them addicted without their knowledge.