Sometimes saying less is more. Choose your words carefully - they might be hard to say. If you're worried about him, tell him that. Say, "I'm worried about you."
If you care about him, if you love him, say that too, "I love you. I care about you, and I want you to be safe."
If you want to give him permission to open up to you, maybe say, "Can you talk about it?" and listen. Sometimes the best way of showing you care about someone, is to listen to them. And who knows? He might have very little to say, or he might have a lot to say, and it will probably mean a lot to him that you listened.
There's ways of showing you care physically too. If you both feel comfortable, you can give him a hug. Or even something as small as touching his hand. I'm sorry; it sounds like both of you have been in some very painful situations. Do what makes you both feel safe. Remember; the love is still there.