One in four people will at some point suffer from mental illness, which can be really difficult when it’s your friend (or you). It is hard to balance friendship and helping someone who is unwell. The most important thing is making sure that you keep yourself well. If helping someone with their problems is starting to impact your own physical health, you have to pull back and take care of yourself above all.
I think the most important thing to do if a friend tells you they are suffering is insist that they need to get professional help. There is no way that you can make them better because you are not a trained professional and you are not a neutral party. Everyone needs to get stuff off their chest and talk to their friends, but friends cannot replace a doctors advice. Friends cannot perscribe medicine, or therapy, or diagnosis. When you are friends with someone you can’t give them the proper care they need. If someone is refusing to get the help they need (and people will, especially when they are over 18 and can do so) it is not your responsibility to step in. However loyal you are to them as a friend, or however much you love them, insist they get help or step back (easier said than done). It is not selfish to be unwell, but it is selfish to put undue stress on people who love you because you will not try to get better.
That being said, if your friend agrees, help them through the process. Going to an appointment alone (especially the first one) can be scary and a lonely feeling. Someone times, all it takes is a text to say that you hope it went well, or a coffee after to make a massive difference to someone who probably feels quite isolated already.
If someone you know is a danger to themselves or others, forget what they will think of you and whether they will be angry at you and call an ambulance/ the police. When people are really unwell rationality goes out the window. The guards/parmedics can do wellness checks and will evaluate whether the person needs to be in hospital. If you are worried about someone it is for a reason. Likewise, if someone is not in immediate danger but is acting recklessly and could endanger their own life, call their parents, even if they hate you for this. If you don’t feel comfortable talking on the phone (especially if you don’t know them), message a brother/sister or a friend from home who could talk to them.
Listen to them, but don’t become a person to vent too. Its easy to become wrapped up in your own problems and not see the light at the end of the tunnel. Talking to people about how you feel when you are really unwell can be validating in a bad way- in your heart you don’t believe you are sick and need the validation of hearing someone say that you are to feel slightly better about yourself. This is fine when it is in small doses, but ultimately it isn’t improving anything and can make it harder to get better because being ill can become part of your identity when you feel like you don’t have one. If someone seems to be doing this, it isn’t good for you our the person. With any illness it is good to be able to talk about it, but there is no way you can feel better if it is all you talk about. If a friend is doing this (especially if they are not willing to speak to a professional) nicely explain that its isn’t good for your mental health to be under so much stress taking care of them and worrying about them and you’re sorry but you have to take care of yourself.