Are men in the seminary, training to become priests, required to be celibate?

I know priests aren’t supposed to have sex, but what about when they are still in the seminary, en route to the priesthood? I went home with a guy the other night, and when I left, I found that I was actually leaving a seminary. After consulting someone who knows him, I found that he is becoming a priest. I got very confused about what I had just done after hearing that, for sure. Does anyone know what the rules governing pre-priesthood are?