Please accept my apologies as I was not clear if you were just venting and otherwise fine or if you do NOT want to be angry and bitter anymore.
I absolutely know people I cam convinced are happy and feel normal with anger.
Ok, so, this #### is simple which is not to say easy. It is a conscious choice, for now, to CHOOSE to not get angry or bitter. You work at and change what you can. The rest, you either accept and refuse to take the bitter path or you don't. Vrai's 'get over it' is accurate enough but doesn't offer much in terms of mental process.
Do some reading on the word 'contentment' and see if that is helpful. Inner peace man, I found it a few years ago. Every single decision you make directly affects it. It becomes easier over time, with practice. Being human, it can still come back which is really no fun but I've found it is VERY easy to choose out of it.
It may well require some people and/or other changes. So to speak, it's a lot harder to stop drinking if you spend a lot of time at the bar. It's harder to be at peace with negative people in your life. It is MUCH easier to live with less stuff, money, things and not have negative people in it than to live with the extra stuff and have to pay for it by having a negative person(s). Lots of people can find their compromise. Some can't. All about choices and that is the FIRST step; accepting that YOu get to choose.