Life happens.
People are going to make mistakes no matter what. Sometimes these mistakes aren't that bad in the grand scheme of things. But sometimes they are, and it can be challenging to watch someone you care about make those big mistakes.
Here's what you can do to look out for yourself, while still supporting them.
Decide how involved you can afford to be.
You have your own life to live. Do not be ashamed to live it, even if someone else is in a crisis. Deciding how much of your time and energy you are willing to dedicate to this person will help you set your boundaries which are crucial to making sure you don't burn out.
Set your boundaries.
More importantly though, stick to those boundaries. If you don't stick to your boundaries, what's the point of even having them? Your boundaries are there to protect you, and regardless of what is going on around you, that should always be your number one priority.
Understand that they are not your responsibility.
You are not responsible for what they do or do not do. If you provide them resources that they can utilize to help themselves, and they choose not to use them, that is not your fault. It isn't that the resource wasn't good enough, or accessible enough, or anything along those lines. They make their own choices, and you are not responsible for those choices.
Remember that they will likely be unable to give what you need from them in your relationship.
They are working on themselves, and that means everything (and everyone) else may get pushed to the sides. You haven't done anything wrong. They don't care about you any less. They are growing and, as all growing things do, they need the space and grace to do so. Grant them that space and grace.