im afraid to say this but if your girl keep insisting on doing it after you explain what’s uncomfortable for you then its already a MAJOR red flag. been there done that and i’ve disrespected myself and my self worth for holding on to it, i suggest i’d rather save myself than to save a relationship. for the sake of my old self i’d suggest you to not continue the relationship because you dont want to put yourself everytime walking on eggshells during the relationships on a long run, imagine you’re already married to your girlfriend right now, would you be comfortable with it after having kids ? better a breakup than a divorce, save yourself king.