wow, this must be hard.
you've already shown you're supportive though by saying you're there for him, and as long as he knows this - it's really up to him to choose when he wants to speak to you about it.
as you say, things are different now that you're not his girlfriend anymore, and the fact is it does make things a little awkward as even though you're close, you can't just pop round so freely like you might have done. what he's going through must be awful, so all you can really do is take a step back, give him some space, but also stick around in case he needs support. the pain/grieving won't go for a while, but memories will stay. when he's ready to accept and move on, make sure you're there to help him get back to normal.