Hi. I have heard different opinions regarding these issues: if a woman is not married,and she is alone for many years,she is unable to refrain from ever being with a man.what should she do? go to the Mikveh or sleep with a man without the Mikvah? also,is it worse to sleep with a goy or a jew? and what exactly does it mean that the punishment will be Karet? How can one be expected to live so many years without physical relations?

Shalom, I apologize in advance since I will not answer your question, at least not in the way you might want. I feel like a doctor asked by his patient which drugs he should use, cocaine or Heroin, the answer must be that both drugs will kill you, one maybe faster than the other depending on the individuals unique characteristics. Accursed will be the doctor that allows drug use only because there are even worse substances around. It’s as if you would ask me that you can’t afford a kosher restaurant and you need a rabbi to tell you whether you should have a sea food or a cheeseburger… I don’t think I am in the position to preach since I have not been in this situation but that does not change the facts. Having premarital sexual relations are strictly prohibited according to Judaism how ever way you look at it, whether it is with a Jew or a non-Jew, whether it’s before Mikveh or after. It might be true that relations after Mikveh eliminate some Halachic problems but you gain others if you do go. It’s again choosing between heroin and cocaine and I will not advise you to take one only because the other might not be as deadly. It is hard. Even very hard, especially if you are single, attractive, courted and lonely, yet it is still deadly and eventually will cast only misery upon you. You would rather have bread and butter your whole life than poisoned delicacy roast beef. You will find your match sooner or later and will be so much more satisfied when you come to that permanent relationship pure. Pray to Hashem. He is always there and always listens, turn to him truly and he will not put you down. As for Karet, it is a spiritual punishment, the soul is cut off from the Jewish people, and it has implications within this world such as premature death but mainly will impact ones life after death. You don't want to willingly brink Karet upon your self. Don’t ever forget that Hashem is merciful and there is no sin Teshuvah can’t rectify. All the best