I think (I am sorry to put this onto you) but you may need to use your skill to work out what will be the best approach for him. Could a good friend or family member help to get through to him, or would he be defensive?
Is there any way you can help him recapture the dream of being parents that you had at the start?
I am very sorry for you to be going through this. He really must seek help. If the adoption were to break down what would this do for your relationship together?
"I'm feeling pretty lonely right now." Please do look after yourself, can you access any counselling or post adoption support. I know it is shit but you must stay strong from your dh and your new son.
Does your area have an adoption buddy scheme where more experienced adopters could come along side you? IF such a scheme existed it may be mums and dads. Would another man be able to help support your dh or would this be awful for him?
I am so sorry to say this and I do not want you to say it to him but while I do have a lot of sympathy for him, I am actually rather angry with him.
This little boy has had no say at all in what has happened to him, he has lost his birth family and maybe a foster family too. Yet he is willing and able to trust you and your dh to be his new family.
Your husband, although he is depressed and I can imagine this is very very hard, is an adult who has chosen this path and should be doing everything he can to make this work.
I wonder if he has lost a sense of control?
If this is the case, what would give your dh a sense of control?
Would being able to look at photos and see things are actually getting better? See the journey you have been on.
Or imagining the future?
Talking to a friend?
It may be worth gently suggesting that other men (or women) may feel upset at the arrival of a new baby, other husbands may fear being pushed out etc, so this is not necessarily adoption related.
Bless you - it is so tough. Stay strong.