Ok..This isn't Gonna be a Simple One Answer Entry..There Are MANY Issues Here.
1) Your Girlfriend is relating an Act to a Prior Experience Having Nothing to Do with You that is Painful To HER **Although it gets on Your Nerves Clearly and Understandably** So Don't Take it Personally,I KNOW that seems like Alot to Ask.
2) This Former Guy was a JERK Obviously,and she May Not have REally WANTED to Give him Oral, but Gave In,and Feels Ashamed for Having Done so,and Doesn't Want That Experience To Creep into her Loving RElationship with YOU Whilst You're Having SEX... **Hence Resenting You By Association***
3) Bitching and Nagging Her To Give You HEad Isn't Gonna Help Your Case,Even if she Did give in and give you what you want she'd REsent You Pushing Her and You'd feel Bad About her giving you what you Said you wanted in the First Place **You'd be like the guy who gave her the bad memory to Begin with**
4) You're gonna have to Discuss your TRust Issues.
Reassure Her that Oral Sex is Not "Dirty" in your mind and that You aren't gonna see her as "Whoreish" for doing so..That you see the act as "Beautiful" and let her know you will Not look Down on her IF and WHEN SHE DEcides SHE is Comfortable doing it. THEN DROP IT
5) Stop Bringing It UP. **Her Past is HER Business..You Should Feel Privilaged SHe even TOLD You.. Stop Throwing it up in Her Face**
6) REassure Her You Love,Honor and Respect Her, and Her Boundaries ..and SHOW HER. **That Her Happiness is More Important Than Your BlowJob**
And An Amasing Thing Might Just Happen..When You STop Concentrating on The BlowJob You're Not GEtting, After She Feels SAfe,Loved and REspected, You Might Just Get What You WAnt..Without EVER ASking Her.
And When She Does..Praise Her For IT... *In a REspectful Way... Don't Say Something Stupid Like " I Love The Way You BLOW Me Baby"
And Remember, It's Not WHAT You ASK..it's Often The WAY you ASk for things, that either gets you what you want without the other person feeling negative about the situation,or Doesn't Get you What you want At All, or is BEgrudging Given to You and Later REsented **REmember Her EX**
Good Luck.
Last Question you REally Need To Ask Yourself..What's More Important..Her Or a BlowJob??
If It's The BlowJob, You Both Need To Be With OTHER People.