I allowed a female to perform oral sex on me last year. I really feel ashamed because I want to be a pure virgin when I am married. Even though I never had sex (and never want to until after marriage) would I still be unpure when I am married?
Oral sex is still sex. Even though you haven't had intercourse, you cannot claim you are inexperienced at sex, which is what being a virgin means. The fact is that you sinned and committed fornication, but that is not the end of the matter. It is not a matter or being pure when you get married. It is about being forgiven of your sins in the sight of God.
When you are forgiven of sin, you can forget about your past mistakes and press on toward the goal of heaven. "Brethren, I do not regard myself as having laid hold of it yet; but one thing I do: forgetting what lies behind and reaching forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus" (Philippians 3:13-14).
If your girlfriend ever asks you if you are a virgin, be honest: "I once made the mistake of having oral sex done to me and I've regretted that choice."