Husbands, sons isnt his... lost.

My husband was with his high school sweetheart and they became pregnant very early in the relationship. My husband was with her through the whole pregnancy until the child was one year. They broke up because he caught her cheating with his bestfriend, she said the PPD made her do it. He still took care of his son. Me and him began dating and he'd send her 500 dollars every two weeks and had the boy one week on, one week off. We eventually got married the child was two in a half. I became pregnant with twins 😍 right after the childs 3rd birthday the mother cutt of contact because he had "basterd children" well my husband took it to court. He was still paying the mother every other week but wasnt allowed to see the child. Well, last week we found out his son, isn't even his son biologically and the courts now dropped the case. If he wants to pursue he has to find the biological father to get permission to adopt said child but the mother still isn't cooperating, she claims the child could belong to either two other men. His cousin ( which makes sense because the boy looks exactly like my husbands grandfather which is why he never questioned paternity) or a random man, she hooked up with once and never saw again. Now we are stuck this little boy, who my husband raised since day one is not only not his child, but the mother refuses to let him see the kid. My husband is torn and I don't know how to help him. Has anyone been through this before? What have you done, any advise?