Is there any update on your situation??? I am having something similar and dying over here worrying about what it might be. Although unlikely hiv, it could be hpv (herpes) - very likely; and unlikely syphillis cause it takes a looong time to emerge (like a month). There are varius strains of hpv, so its hard to say which one it is and how long it will last...but it MUST be treated.
Did you give the person oral sex?
The original post was made almost 2 full years ago, and it was his only post here, so I doubt you'll get a response.
HPV is human papiloma virus, which is what causes warts and abnormal cells on the cervix, and is very unlikely to cause warts in the mouth. Herpes is hsv, or herpes simplex virus.
How long have you had the sore, and do you have any plans to see a doctor? That's a must if you want to find out what it is.