Student visa application. Should I mention my girlfriend or not?

Is there any reason not to divulge the nature of a romantic relationship when applying for a student visa in the UK? I am about to apply for a Tier 4 student visa to live/study in Canterbury, Kent, where my girlfriend lives. I've always been straightforward with the UK Border Agency when asked about my reasons for entering on a visitor's pass, but now I am worried that it will look like I am only wanting to study in the UK to be with her. If I don't divulge, I am worried that it will look like I'm hiding something. Any suggestions?   

If you actually qualify under the Tier 4 rules then that is all the UKBA will care about. Girlfriend or no girlfriend. I don't believe that there is a question on the application that asks if you're actually going to use your visa to shack up with your girlfriend or not. It's pretty irrelevant actually.

Thanks for the quick response. The question was something like, "Have you been to the UK in the last 10 years.. and if so, for how long and what purpose?" Obviously, it's all down to how one interprets the word "purpose". The reason I am concerned is because I have gotten hassled so much at the border that there is a whole dossier on my relationship and reasons for entering. I agree, it should not be relevant, but my experience tells me different. I just want to be honest and consistent.

I've just moved over on a Tier 4 two weeks ago and have visited my boyfriend 3 times in the past year.  I was worried about the same thing.  On the part of the application you are referring to, I just put the dates of all my other travel and the dates of the visits with the purpose right after.  It looked like this (the "etc" are because I don't want to type the whole thing out over again 

06/10/08-07/28/08 Backpacked through Europe visiting Ireland, UK, Netherlands, France etc....
09/18/08-10/01/08 Glasgow to visit boyfriend
12/27/08-01/07/08 Glasgow to visit boyfriend
etc...

It makes sense to put it since they're asking for the purpose and that was the true purpose of the visit.  You don't need to launch into any lengthy explanation or anything. Plus I'm sure they're already going to have your UK immigration history available so it's not like they aren't already going to know.

It is anything but unusual for student visa applicants to have girl- or boyfriends in the UK.  As long as you meet the requirements for the visa, it won't matter.