HPV (human papillomavirus) is the virus that causes genital warts and it is hard to know when it was passed to you. We generally say that it can take 1 to 8 months or longer for genital warts to appear after HPV has been passed to someone.
It’s possible that the warts could have appeared earlier but were too small to see and only recently became big enough for you to notice.
You also said that your bf was a virgin; I don’t know his full sexual history but HPV can be passed with oral sex and sometimes people consider themselves a virgin if they have not had vaginal sex, but oral sex does not count.
Given that HPV is so common and most people don’t get symptoms it can be very difficult to know from whom or when the HPV was passed to you.
With what you have written I would not say that there is evidence that your bf cheated on you. Have you been able to discuss this with your bf?
Here are some links for some more information on HPV.
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