Hi mary_ittls. I am in a somewhat similar situation. I have been in a monogamous relationship for six years. My boyfriend is the only person I have ever had any sort of sexual contact with. About 15 months ago, he was diagnosed with a genital wart. I completely trust that he has not cheated on me, so we can only assume that either he has had hpv since before we started dating and it took this long for it to become symptomatic, or that he was misdiagnosed. He was previously diagnosed with another skin condition--molluscum contagiosum--before we met, so there is a slim chance that the bump at the base of his penis was this, or even just a regular bump (his skin is very prone to moles and bumps in general).
I could babble for a while about the specifics of our situation, but to specifically address your problem...
First, it is within the realm of possibility that the hpv (whether the high-risk cancer-causing type or the low-risk wart-causing type) has been dormant in either one of you until now. In other words, since you have had previous partners, and I assume your boyfriend has as well, it is virtually impossible to determine exactly when and from whom either or both of you may have been infected.
Second, I strongly suggest that you tell your boyfriend. I understand how uncomfortable that may seem, but if you hope for a long-term relationship with him, it seems like the only reasonable option. What if he develops warts later and tells you? You'll either have to admit that you've known for some time about your own infection or lie. What if you become pregnant? There is a very slight (i want to emphasize very slight so I don't freak anyone out) risk of transmitting hpv to your baby, which will need to be discussed with your obstetrician. Would you keep your boyfriend in the dark about this, too? What if you break up? Your boyfriend could unknowingly expose any future partners. Finally, how would you feel if you found out that your boyfriend knew that he had hpv, and/or warts specifically, and decided not to tell you?
One more thing about my situation; my boyfriend was diagnosed with a wart about 15 months ago, but he didn't tell me until about 3 months ago. The fact that he didn't tell me is much more upsetting to our relationship than the fact that he has warts. I understand that he didn't know about the warts before we started dating, so if he had told me when he was diagnosed, all we would be dealing with would be the hpv itself. Now there is a huge breach of trust that i'm not sure I can get over. I think you're risking the same situation if you don't tell your boyfriend.
Finally, here's a website with the best information i've found on hpv as well as many other stis (and i've spent many hours reading lots of crap):
www.Ashastd.Org