It’s so hard.
Some of what has helped in our house is lots of listening, but subtly steering towards a special interest. The depression becomes a special topic of its own, so I try to listen, validate but also change the record if I can.
Paying attention to the sensory diet - reducing as much dysregulating stimuli as possible and increasing regulating input. This has been more impactful than psychological therapy,
Movement- motion changes emotion. Tossing a ball or taking a walk. I never suggest that it will make him feel better, or he would resist it, but if he wants to talk to (at) me, I invite him to follow me, to get him up and moving.
Not to minimise in any way, but it was very helpful to me to understand that he could get dangerously low quickly, but also come out of it rapidly too. Depression didn’t move as slowly and consistently as it would for a neurotypical - it was a spikier experience. It helps me not panic (as much) in the awful lows.
Watch that he’s eating (something/anything) and hydrating. Any kind of physical or sensory stress magnifies big emotions.
In terms of support, ds has needed me to advocate for him at times. I talk for him, until he’s ready to take over and then fade back. Sometimes I’ve attended sessions when he won’t and just done my best with whatever they’ve suggested
Can you identify any specific anxieties? It’s not unusual for dc with autism to find some thing unbearably hard, that might go unnoticed by us. And very often, there are alternatives, work arounds or things that can be avoided. It’s like taking rocks out of their path.
Not sure if any of that is useful as it’s quite specific. But sending solidarity,