Being true to yourself: It's important not to blame yourself for a loved one's choices, or even for behaviors they don't have a choice in. Don't make it all about you, but don't make it all about them either. Take care of yourself, don't ignore your own boundaries. No matter how unable they are to change, it doesn't mean they get to call the shots when your well-being is at stake. If you can stand your ground in a way that is safe for them, do so. Keep in mind that allowing someone to be a tyrant doesn't save them from anything, it only makes you both more miserable.
Be true to your loved one(s): Loving unconditionally can be very hard sometimes. If you are able to continue a relationship with an unwell loved one, work to take yourself out of the equation. Try to avoid occupying the bulk of your time with them nagging or waiting for an opportunity to force change. Your interactions with them may require some coffee talk. Think about what is important to them and talk about that when you feel tempted to push them towards seeking help yet again. People require your transparency. It allows them a safe space to be the best they can be.
If you need to, however, don't be afraid to distance yourself from them or cut them off entirely until they express an earnest desire to get better. Let them know, in a factual manner, why you won't be around as much, if at all. Tell them that when they are ready to change you'd be happy to help, but until then you must meet your own needs. Some people have to come to a decision themselves, no matter how dark things may get for them. Sometimes, as in my own case, people must hit rock bottom before they reach for the light, so to speak. One firm request for them to seek help may not have been as disregarded as you may believe. When and if they come to the decision themselves, they may have more of a chance of listening to you in the future, whether or not you ever know it.
None of us can know what processes go on inside another person.