If you ask me, its not actually that hard to control ones own sexual urges. I can understand how it is for you to stay virgin and away from your fiancée but thats where the fun is, its kind of a tease and when you get married, the result would be so fulfilling and amazing with your pent up feelings coming to life, you guys can have a whale of a time. As of now, take your mind off sex.
I’m sure you got enough of work on your platter, so concentrate on that rather than having thoughts on sex which are kind of turning into an obsession for you. Take your mind off it and concentrate on other things that you find good. You can engage yourself in some activity maybe, you can prefer to not stay alone and idle for most time etc......
Having thoughts is good, it helps take the edge off, but having thoughts on a frequent basis would take form of obsession and might actually disturb your life, so know your limit and act on it. And you’re 27 and your girlfriend is 30, I presume you guys are pretty much settled in your respective careers, so why don’t you get married?