It's certainly a very fine line to walk gooseberry.
What I've gained most so far out of this important thread is that, once again, there are no definitive right or wrong answers. The PALS have given some important insight of their own feelings and responses to the disease. These may have some bearing on your Steve and what is going on.
I think firstly for you, it hinges on the kind of relationship you had before ALS. That will influence how you approach things with him for yourself.
Secondly, I personally think Julien has some deep insight for one so young. He is being hyper-vigilent, and yet sees a need for respecting some boundaries he perceives. What a treasure he is!
I am just guessing, but if you received information he doesn't have, then maybe it has to be weighed, by you, on the lines of - what are Steve's ultimate wishes, against what this information you have means. (I'm not asking you to tell us, but to think this way) If it means you know things about how fast progression is or something about prognosis and it won't help Steve live what he has with quality, maybe it is best just keeping to yourself, or sharing with someone you can trust just to talk about it.
If it is to do with something that could improve his quality, maybe you can find a way to discuss it with him from a quality of life perspective.
We have had some threads at times about 'what is quality of life anyway' and this is another thing that differs for individual PALS, and also may differ for the PALS and CALS in a relationship.
I feel like I could go around in circles, but I do feel strongly about this 'no right or wrong answers or strategies' as something that fits everyone. The sharing of so many views here highlights that, and gives extra perspective as you work out your own situation.
In the end, does it matter if he is in denial or confused? Either could be as difficult to deal with. In denial would mean he does not want to discuss these things, it probably overwhelms him. Confusion could mean he won't understand if you try to discuss at length. Damned rocks and hard places.
Lastly, maybe it's worth weighing up from the view of - how will you feel afterwards. If you can find that place of acceptance of what this disease is doing and will do, and work on what you can do something about, and allow Steve as much control as possible, you will always know afterwards that you did these things out of love. This is regardless of what the actual details of each part of each situation are.
I really appreciate the difference in the tone of this thread here with both PALS and CALS being in the discussion, compared to a CALS only group. It has enormously broadened the horizons of my thinking!