Shulchan Aruch, Even Ha'Ezer 16. Here’s a rough translation:

A Jewish man who has relations with a gentile woman in a way of marriage gets Malkus (flogging) from the Torah, as it says "thou shall not marry them". But one who has relations (as a one time thing), is chayev on the Issur Derabanan of "Kusis" (non-Jewish relations) and "zonah", and he receives "makas Mardus" - (flogging de'rabanan). And if he designates her as a "girl friend" for him, (not for marriage but also not just as a one time thing), then our Sages made a gezeira (See Gemara Avoda Zara 36b – from Beis Chashmona'im, which preceded the Mishna by a few hundred years!) that he is chayev on Nashga"z, which stands for 4 different Issurim derabanan: "Niddah", Shifcha", "Goya", "Zonah".

Also, (one who has relations with a non-Jewish woman, zealots may kill him during the act, as we see by the story of Pinchas. This is Halacha LeMoshe Mi’sinai – Kana’im Pogim Bo) if he was not killed by zealots and did not receive flogging by Beis Din, his punishment is clear in Tanach that he is chayav Kares, as it says: "For Yehudah has defiled the holy by loving and having relations with gentile women and Hashem will "cut off" (Kares) the man who has done thus…”

Until here are the words of the Shulchan Aruch.

You can also see the same Halachos in the Rambam, Hilchos Issurei Biyah, Perek 12.

Besides for this, The Gemara in Avoda Zara 5a writes that when a person transgresses a sin (with a non-Jewish woman), she is bound to his soul in the next world like a dog… Like it says by Yosef Hatzadik, that he didn’t listen to the wife of Potifar “to lay with her, to be with her”. (The Gemara learns from the double wording): “To lay with her in this world, and to be with her in the next world”.

The Gemara in Eruvin 19a writes that Avraham Avinu sits at the entrance of Gehenom and pulls out from there those who needed to spend some time there, besides for those who had relations with non-Jewish women. This is because when he is with her, she pulls the fore-skin of his member upwards (she doesn’t like that he had a bris milla) and therefore Avraham doesn’t recognize him (to take him out of Gehinom).

The Maharil explains this simply to mean that when a Jewish man is with a non-Jewish woman, he wishes he would not have had a bris mila, and this “wish” cuts him off spiritually from Avraham Avinu who was the first to make a Bris Milla, and therefore Avraham doesn’t pull him out of Gehenom.

 Shulchan Aruch, Even Ha'Ezer 16. Here’s a rough translation:

A Jewish man who has relations with a gentile woman in a way of marriage gets Malkus (flogging) from the Torah, as it says "thou shall not marry them". But one who has relations (as a one time thing), is chayev on the Issur Derabanan of "Kusis" (non-Jewish relations) and "zonah", and he receives "makas Mardus" - (flogging de'rabanan). And if he designates her as a "girl friend" for him, (not for marriage but also not just as a one time thing), then our Sages made a gezeira (See Gemara Avoda Zara 36b – from Beis Chashmona'im, which preceded the Mishna by a few hundred years!) that he is chayev on Nashga"z, which stands for 4 different Issurim derabanan: "Niddah", Shifcha", "Goya", "Zonah".

Also, (one who has relations with a non-Jewish woman, zealots may kill him during the act, as we see by the story of Pinchas. This is Halacha LeMoshe Mi’sinai – Kana’im Pogim Bo) if he was not killed by zealots and did not receive flogging by Beis Din, his punishment is clear in Tanach that he is chayav Kares, as it says: "For Yehudah has defiled the holy by loving and having relations with gentile women and Hashem will "cut off" (Kares) the man who has done thus…”

Until here are the words of the Shulchan Aruch.

You can also see the same Halachos in the Rambam, Hilchos Issurei Biyah, Perek 12.

Besides for this, The Gemara in Avoda Zara 5a writes that when a person transgresses a sin (with a non-Jewish woman), she is bound to his soul in the next world like a dog… Like it says by Yosef Hatzadik, that he didn’t listen to the wife of Potifar “to lay with her, to be with her”. (The Gemara learns from the double wording): “To lay with her in this world, and to be with her in the next world”.

The Gemara in Eruvin 19a writes that Avraham Avinu sits at the entrance of Gehenom and pulls out from there those who needed to spend some time there, besides for those who had relations with non-Jewish women. This is because when he is with her, she pulls the fore-skin of his member upwards (she doesn’t like that he had a bris milla) and therefore Avraham doesn’t recognize him (to take him out of Gehinom).

The Maharil explains this simply to mean that when a Jewish man is with a non-Jewish woman, he wishes he would not have had a bris mila, and this “wish” cuts him off spiritually from Avraham Avinu who was the first to make a Bris Milla, and therefore Avraham doesn’t pull him out of Gehenom.

 Shulchan Aruch, Even Ha'Ezer 16. Here’s a rough translation:

A Jewish man who has relations with a gentile woman in a way of marriage gets Malkus (flogging) from the Torah, as it says "thou shall not marry them". But one who has relations (as a one time thing), is chayev on the Issur Derabanan of "Kusis" (non-Jewish relations) and "zonah", and he receives "makas Mardus" - (flogging de'rabanan). And if he designates her as a "girl friend" for him, (not for marriage but also not just as a one time thing), then our Sages made a gezeira (See Gemara Avoda Zara 36b – from Beis Chashmona'im, which preceded the Mishna by a few hundred years!) that he is chayev on Nashga"z, which stands for 4 different Issurim derabanan: "Niddah", Shifcha", "Goya", "Zonah".

Also, (one who has relations with a non-Jewish woman, zealots may kill him during the act, as we see by the story of Pinchas. This is Halacha LeMoshe Mi’sinai – Kana’im Pogim Bo) if he was not killed by zealots and did not receive flogging by Beis Din, his punishment is clear in Tanach that he is chayav Kares, as it says: "For Yehudah has defiled the holy by loving and having relations with gentile women and Hashem will "cut off" (Kares) the man who has done thus…”

Until here are the words of the Shulchan Aruch.

You can also see the same Halachos in the Rambam, Hilchos Issurei Biyah, Perek 12.

Besides for this, The Gemara in Avoda Zara 5a writes that when a person transgresses a sin (with a non-Jewish woman), she is bound to his soul in the next world like a dog… Like it says by Yosef Hatzadik, that he didn’t listen to the wife of Potifar “to lay with her, to be with her”. (The Gemara learns from the double wording): “To lay with her in this world, and to be with her in the next world”.

The Gemara in Eruvin 19a writes that Avraham Avinu sits at the entrance of Gehenom and pulls out from there those who needed to spend some time there, besides for those who had relations with non-Jewish women. This is because when he is with her, she pulls the fore-skin of his member upwards (she doesn’t like that he had a bris milla) and therefore Avraham doesn’t recognize him (to take him out of Gehinom).

The Maharil explains this simply to mean that when a Jewish man is with a non-Jewish woman, he wishes he would not have had a bris mila, and this “wish” cuts him off spiritually from Avraham Avinu who was the first to make a Bris Milla, and therefore Avraham doesn’t pull him out of Gehenom.