why is britain so depressed Watch
We are not depressed about the weather - its actually better then its been in the past thanks to global warming.
Brexit is a factor definitely, we are lacking in hope/optimism at the moment, and brexit contributes to this.
Your last bit about LGBT stuff is just weird and not relevant. The UK on the whole is incredibly accepting and friendly towards LGBT people, and given that they are only a small percentage, even if they were all unhappy and treated badly (which they are not) it wouldn't shift overal national happiness to much.
Why are we getting more and more unhappy? Mainly because we have forgotten the key things that made us happy - one of the largest being our family and our community. Countless studies show that being surrounded by people you love, both in your family and in your local area impoves happiness and wellbeing drastically.
So knowing this, what are we doing? We are on average living further away from our family then ever.. we are interacting less with our local communities then ever.. we are marrying less.. having less children.. etc. etc.
The proven joys of family and community have been replaced by career and possession, and generation by generation we are finding out that for the vast majority of people, their careers and the things they own are not enough to give them a fullfilled, meaningful and happy life.
that is why Brexit is so popular; it gives life's losers the chance to spit in the face of the successful ones.