My husband adopted my son a month ago, since then me and my husband split up can so since its only been a month ago since he had adopted my son is it possible to have the adoption undone?

No, not unless there were someone else to adopt. He accepted the children and now they are his.

An adoption takes a significant amount of time to process. I doubt if things would have all of a sudden gone south in a month. So its likely he was aware of the strained relations when he signed the adoption papers. Which makes it likely that he won't be allowed to recant.

Most likely no, unless there can be found some legal error in the proceedings.

So now, he will be the one paying the child support, or the one to get joint custody of the child. Just the same as the bio father would have had to.

He is now the legal father with all the same rights and duties as the father.

And Scott is correct, in one month things just don't change, so last month when adopting, why did you not put it off ?