Does this mean the BF has fucked her many times already ?
It depends on what her perspective of a man visiting a prostitute. If she sees it as a moral issue, what is the moral issue ? If she thinks fornication is wrong, then she herself must not have sex with the BF before or outside marriage. If they have already started fucking before marriage, then she does not have any moral authority to judge on the issue of BF visiting a prostitute.
If she is not happy because the BF used to pay for sex, and she feels disadvantaged because she is not paid by the BF, then the issue is more simpler. She can demand the BF pay her every time they have sex.