Should we get a second opinion on HIV test results?

My fiance and I have been together 3 years, never used drugs, and have not had any other ual partners but each other in our 3 year relationship. He is 31 years old and I am 26. He recently went to have a check up at his new provider , where they performed a routine examination and a blood test. He was not aware he was being tested for HIV, just thought it was a regular blood work test because it was a new dr. When he went in for the results, the dr told him that they had tested his blood for HIV and got "abnormalities" on the test, so they tested it again and it tested postive for HIV. Of course we are devastated...and confused/shocked! I immedietly went in to be tested. My test came back negative, but I was advised to be tested again in 3-6 months just in case I have been recently infected by him and am in a window area. My question is, how, after 3 years of unprotected ual with only each other and no other risk factors in our lives, can he have HIV and I dont? It doesnt make any sense to me, as he has had zero exposure in 3 years! Should we get a second opinion or another test? I am so scared and confused...but dont want to live in a state denial. He goes back in this week to see an immunity specialest referred to him by the dr to check his viral loads. I am praying for a miracle. Any advice or knowledge would be great.