Yes. Not only can you but you should. You told this man that you didn't want to be in his life. You did that to protect yourself. He is not your responsibility. Not only that but he has people looking out for him.

Even if he did not you don't owe him anything. He has an addiction that he isn't dealing with. Why did he message you anyway? If he was looking for help surely he would contact someone who was more certain to respond. If he wasn't looking for help and truly intended to hurt himself and just wanted you to know then that's a dick move because it is designed to make you feel bad. If he wasn't intending to hurt himself then it is pure manipulation and he should be avoided.

There is no version of this where you should remain in touch with him.