Peculiar, you sound very like me - I'm dating someone (albeit I'm living with him, so that makes it a lot harder - not for too much longer lately), and somedays, it would be very easy to just let emotions take over and find ourselves in a place we don't want to be.
I guess lately, it's kinda like the lust thought is a baseball, that I have to hit as far away from me as I can (I work in word pictures sometimes, forgive me). The thought crops up, and I use everything in my power to get it outta there. Last night I was commanding lust to flee (rather loudly in my bedroom) from me in the name of Jesus Christ, and that seemed to work.
Sometimes I need to get out and go for a drive. The last couple of times I have done this, I've taken my boyfriend with me, and it's inspired a lot of really good talks. We'll go somewhere and park the car, and then take a long walk to a lookout or something, and talk a bit more about it, and how we can each help each other out when the temptation gets too much.
Another idea is to think about who it benefits - more often or not those thoughts will all be about bringing YOU pleasure, rather than blessing your partner. That's something that stops me right in my tracks. I know that waiting and preventing things from getting out of hand will help us in the future whilst we are still developing a healthy relationship - and in reality, 4 years or so of celibacy now is not that long, when I think of our future marriage, and how long that will ultimately last for.
Sasch