partner`s visa help

[poolswater]

I am a student from Kenya studying in the UK for 3 and a 1/2 years. I met with my girlfriend and have been living together for around 2 and a 1/2 years ago. She is English by birth and works fulltime. She bought her own house about 7 miles away from my place but her daughter lives there although she lives with me because it is close to her work place.
I recently applied for a partner`s visa but was turned down because of lack of sufficient documents to show we have been living together.Unfortunately her documents all go to her own place and my mail comes to my place so we are lacking in documentary evidence to show we have lived together for 2 years.
Below is a list of documents submitted;

1. postmarked envelopes showing letters addressed to her at my address.
2. Landlord`s letter to show she has lived her for more than 2 years
3. Letters from companies associated with both of us
4. letters from friends
5. dated photos for both of us.

Any help as what step I should take.

[Chess]

Habari Mzee Poolwater...

You have to provide sufficient documenatry evidence of co-habiting for 2 years...

Also; perhaps it may be a good idea to get married...