How should I prepare him for a separation?

I posted here before. Husband with BPD. I love him. So much. When it's good it's amazing. But when it's bad, he push me away and goes into a anti social mood so bad, I don't feel like his wife anymore.

Things changed for us during the last 2 years. He used to talk to me. Let me in. I felt a part of his life and his struggles. Not anymore. He does his own thing. I feel like he's a stranger in our house.

Every time I ask him. Do you still love me? He says yes. Tells me I'm the most important person in his life. Yet, acts cold and distant more times than none.

I always hoped for us to find a way to work together. We love the same thing. We used to make plans about our future. But I feel like he's getting harder and harder to reach now.

This is just an example. But he used to send me memes and random photos. I haven't received anything from him in months. I used to be his FP. So many texts. That's gone now.

That's how I know. He used to show me he loved me with his own ways of saying I love you. He doesn't anymore.

He's always been depressed and suicidal. I want to prepare the terrain. In a way a person should be prepared as a BPD.

How can I do that?