Why do you think you gave it to him? And why are you not worried about getting it from him? Herpes is a virus and can result in a cold sore. There are mutiple ways someone could have gotten it, from sharing a drink with a friend, or from making out. Just eat right, get some sleep and it will keep your immune system working to battle you getting it.
See a doctor now.
Where on the genitals or on the mouth? Genital herpes can be treated with antivirals, which you'll need to get from a doctor, or family planning clinic, they can advise you further.
Oral herpes (cold sores/fever blisters), you can get cream from a pharmacist, avoid kissing anyone, sharing glasses or towels for 7 - 10 days (these are actually common and many people suffer with them unfortunately, you can catch it from someone who has no active signs before the sores appear). Once you have herpes you always have it and tend to have break out's. You have caught it from someone else.
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