Herpes from my partner?....

Recently, I was prescribed antibiotics for my UTI. It was accompanied by some bleeding that was abnormal, so I set an appointment with my OBGYN to be safe. Today, when I went in, my doctor checked and said that it could be herpes causing my irritation (on top of the UTI). I've only had two partners: My first was years ago and he lost his virginity to me as I did to him. My current one is overseas, and we only see each other every 6 months or so and the last time we had intercourse was months ago. I don't understand how it could be herpes unless he slept with someone who had it and now it's affecting me?!