As to Brexit, nobody is being forced to accept it has happened and are free to stay bitter until the end of time, but it will do no good, nor do you any good either.
I would dispute that staying "bitter" does "no good". The Eurosceptics have kept up their bitterness over our membership since 1975-ish.
... and they won in 2016!
Personally, I'm not "bitter" - which implies a negative 'sour-grapes' attitude. I am angry, and fired-up to fight back.
Bitterness eats away at your soul, anger can be cathartic - it can also be tamed with some individuals (like me). I accept that Brexit has happened and has to be dealt with. I have no illusions / delusions that we will rejoin any time soon, and certainly not in my life-time. But my anger propels me to fight for a more civil and friendly relationship with the EU which, I believe, would be more positive than this current negative, anti-EU rhetoric, emanating from the Tories and fostered / encouraged by the right-wing media,
My anger is productive and, because of that, it doesn't consume me. Nor does it dominate my life.
I am, as you will realise, taking the use of the word "bitter" to task...