I wouldn't mention it. And I say that as someone who caught Herpes from their husband. 
To clarify, there are two types of Herpes Simplex (as others have said) HSV1 and HSV2. They are the same, the only difference is where they prefer to live in your body.
HSV1 prefers the nerves at the base of your brain, HSV2 prefers the nerves at the base of your spine.
HOWEVER, both can live in either place. However, if they are not in their preferred area you will have fewer, milder outbreaks (usually no more than one in your lifetime) than if they are in their preferred area. If they aren't living in their preferred area, the likelihood of transmitting it to another is also negligible.
HSV1, if living in its preferred place, causes cold sores around the mouth. Depending on the person these can be severe or mild. Someone with HSV1 of the mouth, can transmit it to someone who does not have HSV1, and it can go to the genitalia or the mouth. IF it goes to the mouth (where it wants to be) it can cause severe repeating outbreaks and the person can pass it on to other people. IF it goes to the genitals, the person will most likely get one or two moderate to mild outbreak around the genitals, usually within 2 to 3 months of exposure, and that's it. And if you have HSV1 in its preferred area, you can transmit it without having a cold sore! It's called shedding and its especially common when your immune system is low (i.e. you're sick). If you have HSV1 in at the base of your spine you are unlikely to pass it to someone else, even to their mouth.
I got HSV1 at the base of my spine and had one moderate outbreak, after my husband, who gets cold sores around his mouth occasionally, and I did the deed while we were both recovering from swine flu (this was after 5 years of marriage).
HSV2 is the exact same. If you have it in its preferred area you will have more/severe outbreaks and can pass it on to another persons mouth or genitals, and can pass without symptoms. If it's not in its' preferred area, you are unlikely to pass it on and will have fewer/milder outbreaks.
Doctors estimate AT LEAST 80% of the population has HSV1 or HSV2. Normally, when tests are done doctors just test to see if there are any antibodies in your blood. If antibodies are present, you've had Herpes for at least 6 months and have had at least 1 outbreak (even if it was so mild you didn't notice it). If there are no antibodies, it's a new contraction. They will rarely bother trying to find out if its 1 or 2 as that's an expensive and needless test.
You will always have some kind of an outbreak within 3 months of contraction, regardless whether it is HSV1 or HSV2 or where you've contracted it.
Doctors do not consider it an STI, at least not in the same way as others, as it's really the same virus as shingles. I know this, because I live in the Middle East, and I was petrified that the doctor would report myself or my husband for adultery (which neither of us committed), which is punishable by law. She laughed and said it's not even considered an STI in the country and she would be laughed at if she reported it as such.
OP, chances are he already has it or you have HSV1 and therefore can't pass it on anyway. Either way, it's not worth worrying about because it is quite literally a cold sore.