You can try to help your friends who have mental issues, but it comes with risks.You should know when to stop. I'm not telling you to abandon your friends who need help. Try to support them, but only within your limits.

You're (probably) not a professional therapist, so you don't really have the means to make the kind of impact you're hoping to make. Try to pay attention to the signs when the relationship is beginning to harm your well being. When you notice that, it's time to step back.

If you know someone who clearly needs help but refuses to seek it, you're in a tough spot. Realistically, there might not be much you can do to help. Coming to terms with that that is painful, but watching someone collapse and implode is even more agonizing.

Positive side: You've done what you can, but sometimes that just isn't enough. It's not your fault if someone gravitates towards an otherwise avoidable disaster, so don't blame yourself.