So you are paying almost £800 month for a tiny part of a shared house? That sounds like too much, you could get your own single bedroom place for that much.
You can get 1 bed flats in Brighton for £750 but they tend to be on the scraggy end and you are looking at £800+ for anything decent. You will get somewhere fairly modern in Haywards Heath for £750 but then you would be living in Haywards Heath.
Its recommended that you don't pay more than 1/3...
Except our economy is propped up on the property industry (as well as unsecured consumer credit) and if you flooded the market with new homes and devalued houses the whole economy would be catastrophically ****ed. The government and housing industry have a vested interest in building up land...