All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
What your friends told you is not right because what you did is Zina (fornication or adultery) which is forbidden in all monotheistic religions. Indeed, Islam considers Zina as a grave major sin. Allah Says (what means): {And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way.} [Quran 17:32]
We do not see any good in your having any relation with this woman who commits Zina. Know that if she accepts to have sex with you, this means that she accepts having sex with many other men. This is not in accord with the life the Muslim should lead. In fact, the Muslim should not build a family on a wrong base.
On the other hand, this woman is Jewish and the Jews are known to be traitors and dissolute.
Now, you must repent to Allah from this major sin and end all relations with this indecent woman. Then you should look for a good Muslim woman to marry. Allah Says (what means): {And a believing slave woman is better than a polytheist, even though she might please you.} [Quran 2:221]
Know also that the perverse and bad environment where you live is one cause for your falling in this illicit relationship. The other cause is your weak relation with Allah. Fear Allah and abide by His Commands. Allah will provide you with that which is good for you. Use legal means to get a good and pious wife.
Allah knows best.