This is like a boyfriend or just a guy? Unfortunately, you just never fully know, right? I'd personally go ahead and test knowing you will most likely be hiv negative. If you are not in a relationship with him currently, test 28 days or after with a 4th generation DUO test after the last time you had sex. If you are in a monogamous and ongoing relationship with him, maybe both get tested together. That's my suggestion.
Well, you can’t really take his word for it, because he could easily lie or might not know he has something. You can test for things like Chlamydia and Gonorrhea 2-3 days after unprotected sex. HIV they recommend testing 6 weeks to 3 months after unprotected sex and a follow up test in 6 months. More than likely you don’t have anything to worry about, but you still need to get tested for everything including syphillis, Hepatitis, etc. Him being in the military doesn’t necessarily mean he has safe sex practices. They are around women on military bases and in different countries when deployed. So do get tested and practice safe practices from now on. Don’t beat yourself up, because many people have made the mistake of unprotected sex with people they don’t know that well or their status. Just don’t keep making that mistake and move forward with your life.