I went to check out of curiosity. At the sex toy store Holly says she isn't a virgin and last time she's had sex was 3-4 years ago (she's 23) Later she tells Lena and Ivy she had one boyfriend and one girlfriend. The girl was someone she's been friend-girlfriend with at 14, but they only kissed (and later she dumped Holly to hang out with cooler people)Ivy has sex with Holly and Lena unless playing the game wrong and Holly starts the game with 2 notches on her belt a girl in HS and a dude in college.
Having one boyfriend doesn't necessarily mean Holly has only slept with one guy ever, though. But given her personality it's a likely case.