Spiritually speaking, how is it "pre-marital" sex if I'm not going to marry her?

Brilliant!!

"pre-marital" is a mans term. God calls it fornication.

1 Corinthians 6:13, 18

One possible aftereffect is the contracting of a sexually transmitted disease. Imagine the heartache if years later a person learned that a sexual experience has caused irreversible damage, perhaps infertility or a serious health problem! As Proverbs 5:11 warns: “You have to groan in your future when your flesh and your organism come to an end.

You're absolutely right

Pre-marital sex assumes marriage

If you never get married then you the idea of premarital sex doesn't apply to you

Not so great. Sex is meant to be enjoyed in a loving, committed relationship. If you aren't going to marry her, or even thinking about marrying her, then you are having sex outside of those limits.

Pre (before) marital (when you are married)

Having sex before you are married.

Hahahahahahahaha

Once you have sex, you are already married in God's eyes. The official 'marriage' is just a ceremony affirming what is to be done.

Well, Solly Walks Funny NOR★CAL R&S:

Pre-marital sex is most appropriately classified to people who are engaged.

But casual sex outside the marriage relationship is fornication.

And unsolicited or unwanted sex is rape.

All is sin, even the last one if the victim is not crying for help.

All sexual immorality is sin and should be repented of.

So, if you can't help your conduct with your fiancee, then terminate the relationship or get married.

Blessings, Ben Yeshua

You're having sex before marriage. But it's okay, marriage never stopped me from having sex.

Why would you want to have sex with someone you know you are never going to marry?