I think I would hit the roof! This would probably be one of the worst things to happen to anyone, except cheating. I would think he deliberately hid this from me, because he knew of the consequences. It's a really deceitful thing to do to a person, and the first thing I would do is go, no le me rephase that RUN RUN RUN to get checked out.
The problem with that situation is this, sometimes STD's do not show up for a couple of years, like AIDS.
I would probably be really worried about my health mostly.