Evaluate the benefits and compare them to the drawbacks. Here, I'll help you:
1.You can brag that you had sex now.
2. You've had sex, lol.
3. You may have a way to keep getting sex from this girl.
1. It's a little pathetic to do what you're contemplating to do.
2. Possible risk of STDs/pregnancy. If you plan on having oral sex with her like you say, then I suppose you can eliminate any chance of her getting pregnant.
4. This may somehow come back to bite you in the ass.
If the benefits outweigh the drawbacks, then by all means, go for it. If not, then it'd be inadvisable to proceed to have sex with her.