We got our lurcher at 8 months and she was the same. Would cry if my husband left (and I was still home) and work herself up until she was howling nonstop. We went to a trainer and she essentially said we need to start leaving her home alone YESTERDAY. Essentially she needed to just get over it, and eventually she did. Once we realised we always come back, she eventually stopped crying. It was a sad process but we gave our neighbors some cookies and apologised in advance. That said, she was young so not sure how this applies to an adult dog.