Here is the problem: There is little hope that you can really quell your desire to have sex with your girlfriend. This is because you have had a prior history of sex, know what it feels like, and you've had sex with your girlfriend. There is a classic theory paper in psychology from the early 1960s that deal precisely with your issue. It is called, The Appetitional Theory of Sexual Motivation by Kenneth Hardy. He basically says that once people have experience with something that is a normal, behavioral experience, that is highly rewarding or reinforcing, it is very difficult if not impossible to prevent the 'appetite' or desire for it in the future. So married people who divorce who had active, happy sex lives have a nearly impossible time trying to abstain from sex with their next partner---assuming they want to. Your brain has sort of been 'rewired' now because of your prior learning experiences--and given the fact that you have no time line for 'relief' from your feelings of deprivation, there is really little anyone can do to help you not want sex.
You can do a couple of things. One is to talk to your girlfriend about going into couple counseling with you to at least talk about this issue. Explain that perhaps you can 're frame' or better understand and 'accept' the status of your relationship and nonsexual, or she might find some reasons to cope differently with the episode in Afghanistan in Jan. 2011. So some shift in attitudes on one or both of your parts might occur through counseling. The second thing you can do is explain to your girlfriend that you unfortunately, hold very different values about sex than she does and it has become such a strenuous obstacle that it is now affecting your feelings about the relationship and you 'don't believe the relationship can really continue as it does now, into the future'. Something has to change in terms of her interest or willingness to have sex, or it may actually be the case that you have to both find partners who share common core values and beliefs.
Some guys would attempt to change their girlfriend's mind about sex by changing their patterns of affection. That is, if you know what she will allow you to do, you can do all these things for a longer duration of time, focusing exclusively on her, and her level of stimulation, arousal and pleasure. She likes kissing and perhaps back rubs, but what about body rubs or allowing you to caress and touch and rub her in her private areas? What some guys do is try to increase her interest and willingness to engage in more intimate sexual behavior by increasing her pleasure and arousal levels significantly---under the assumption that it will make it harder and harder for her to not 'want more' i.e., more intimacy and possible movement toward having an orgasm. This isn't exactly the most honest or genuine way of persuading your girlfriend to have sex i.e., put her into an increasingly intense, internal conflict between her intellectual decisions about sex, and her emotional desires, but it does tend to work. Guys have to be willing to forgo much pleasure for themselves and spend time learning more about what is arousing to women, and focusing exclusively on their girlfriend's interests, what gives them pleasure, increases their arousal, etc. This of course might be a process that takes several weeks or months of study and practice on the guy's part.
The final approach to the problem is to be upfront with your girlfriend and tell her that since you differ so greatly on fundamental core values about sex, it may be time to reconsider your relationship. It might be a good idea to back away from having an exclusive relationship with one another and date other women and men, with the idea that you could still agree to have this relationship as your primary or most important relationship----at least until the two of you decide whether to get married or not. (Now, I don't know if you want to marry this woman or not. ) This would probably generate a keen distress reaction from your girlfriend and put her in an intense conflict about your relationship, but this is what she may need to experience. She may suggest getting married or agree to sex, etc., rather than agree to changing the nature of your relationship. Under no circumstances would I suggest you try to secretly start sleeping with another woman because your girlfriend won't have sex with you---this is the worst possible decision.
What do you think?