I think thom has good advice, "My advice is to give yourself time. You can't plough on with an adoption in the aftermath of an unexpected relationship breakdown."
But I would still want to ask what may be possible.
I think hidinginthenightgarden is completely right (you will need time to heal and adjust) and this may not be the right time for this little boy to come to you. BUT I agree I would suggest it. I would ask what your options are.
Have you spoken to your husband? I think it is so recent you may not be able to work out your way forward. I think maybe knowing how you want things to go now will help you.
Is there a chance for you and dh to reconcile and is that what you would want, would that mean never going ahead with adoption? Or are you now in a position to walk away from the marriage (yes, I know it was his decision, and not your decision), but are you accepting of it, and now wishing to try to save the link with this little boy?
I think do what you feel is right. Even if the link cannot be preserved, if you want to ask about it, do. Because you want to be able to look back and say you asked the right things and were open to whatever felt right for you.
I have no idea but 5 seems an age that is still relatively young (our little boy was three almost 4 when he came to us and I think was not considered hard to place). But if this little boy is 5, almost 6, would it be easy for social workers/family finders to find a new match?
I just wonder if the social workers would even consider a foster or foster to adopt situation for you as a lone foster carer/lone adopter for this child after you have come to terms with this, and if he is still 'in the system'? It would be good to just know if this is even a possibility.
Do you want to be a single parent, could you finance this? Do you have suitable support from your parents or other relatives etc?
Did you have any idea your husband could do this?
So many questions, only answer them if you wish to, and if it helps you process all this. I am not just being nosy for the sake of being nosy!
I am so very sorry. 