Second opinion. Please consider a second opinion to confirm if the neck node is metastatic cancer from prostate. It is unusual (though not unheard of) for prostate cancer to skip pelvic nodes and bones and skip straight to a neck node.
Not good. Advanced prostate cancer typically spreads to local/regional lymph nodes first including lymph nodes around the prostate/bladder. Other likely initial sites of metastasis include bones (spine). Prostate cancer that has spread to other organs (liver, lung) or distant lymph nodes (neck) is not a good sign, however could still be treatable. You need evaluation by urologist/oncologist.
Cancer. Unfortunately the 2 year survival of someone with metastatic prostate cancer is 40% and 5 year survival is 10%. Sorry.