She talks about these "persistent guys who would stop at nothing" to get a date with her, that the dates "weren't very enjoyable", that her "frame of reference" for dating "isn't the best", and most notably the fact that she's clearly uncomfortable with both thinking and talking about "intimacy and things of that nature". She neither seems like a girl who rushed into sex once and then put up these walls around herself to not rush into it again, or who ever got to the 3rd date with any of these "persistent" guys.
It seems to me to be quite clear as day that she's a virgin, and I don't say this because it's a kink of my mine because it isn't, or at least it's not something I ever really think about, I say this because this game seems to be making it a pretty clear-cut case.
In the context of Jill's character, it makes perfect sense. She's a shy, sheltered, naive girl who has antiquated views on dating "rules" and who is looking for a genuine, sincere, heartfelt connection with the one that she'll eventually give her v-card to.
From everything she's said, it's clear that no guy has come along yet that has been that for her, until now.