The Art Of A Good Facial
Women who are really into semen might love it; wanting to come on your girlfriend's face or another part of her body is perfectly normal and is a widespread male fantasy. Coming on a woman's face is commonly known as "giving a facial," or if you come on her neck or breasts, "giving her a pearl necklace." It's often acted out in porn, and when it's done by a group of guys on one woman, it's called bukkake. If your girlfriend is up for this, give it a try. You might want to put a towel down first since it might get messy. Exercise some common courtesy and let her know right before you pop one off. And be sure she closes her eyes before you shoot because semen in the eyes can sting like hell. Have a hand towel or tissues ready for clean up afterward. You might also suggest doing it in the shower so it's quick and easy to wash off.
On the other hand, some women find the idea of getting drenched with cum disgusting and degrading. If your girlfriend feels this way, you won't be able to talk her out of it. Let her know what you'd like to do if she's on the fence and see how she responds. Tell her it would be an incredible turn-on for you, and talk your way through the scene beforehand, describing to her what you would do and what would happen when you blow your load all over her. Ideally, this would get her hot enough to start jacking you off immediately.
Bonus Tip: Just try and make sure not to get your cum in her eye because it can irritate.