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Since you are virgin and presume your girlfriend is too, there is no fear of being ignorant of the practicalities of sex. As long as you both are well informed and knowledgeable, it is not necessary to have had sex before marriage. There is a exquisite feeling of having sex for the first time on your wedding day.
Se with a prostitute before-hand can never match this experience. The guilt and shame of having paid for sex can never be erased and will remain with you all your life. You begin on the wrong footing, since you think that you are paying for the sex, it is for the woman to provide you the pleasure. This is not true in real life and you are equally responsible to ensure that your wife is pleased and reaches orgasm.
Another serious problem is the comments passed by the prostitute. If she is uncaring and comments about your penis negatively, that thought will always remain in your mind and can even lead to Erectile Dysfunction (ED). This is in addition to the gift she may give you of STD or HIV.
Another problem is that you could get emotionally attached to a prostitute and if the sex was mind blowing you would look for gratification with prostitutes even after marriage. So all in all, never a good idea to visit a prostitute to learn about sex. Why lose confidence. You wife will accept you the way you are.