I want to be there for him as a friend

This is noble, but I’m sorry to tell you that you can’t really do it yet. You broke up less than a week ago and the feelings are too raw.

In a few months, you might have gotten enough closure to be friends, but it can’t happen both immediately and healthily.

I’m very good friends with one ex, but it took literally years after we broke up to be friends. I’m friendly with others (but we don't really care about each other, though we certainly don’t wish each other ill, as a gauge), and that happened much faster after the relationship.