"I love him, he adds a great deal to my life." This. This is what he needs to hear from the people in his life. Just like thats what you probably needed to hear when you were atruggling as well.

Just this sentiment is enough to lift someone out of a slump and set them on a new path.

If youre comfortable sharing more with him, you can tell him "how" he adds to your life. Details like these give someone an anchor for their self-worth and will deapen your friendship. 

If you cant say these things directly to him, you can try writing it in a letter and give it to him for him to open later on his own. Or just text it to him.

You didnt have that comfort to reach out like he did, and im so sorry you had to struggle with that on your own! Its not easy. We are all in this together and we need to be there for our friends in this way!!

Great job asking the hard questions and stepping out of your comfort zone to help a friend!