Its good that you are indulging in a bit of introspection as that seems a trait sorely lacking in so many people today. They take the view that "I am what I am" and thats just perfect. Honestly, I have never been that bothered by people, I can take them or leave them as I find other things much more interesting to devote my time to.
I have dropped out of contact with a fair few people as a result but I have never had a problem with being angry or bitter. If I see them again out of the blue its great to catch up but I just don't find individual people that interesting.
The moral of this is that you need to find out the things that you enjoy and focus on them. If you are happy in your life then you will be nice to people as a matter of course and their actions won't directly impact your happiness as much. Looking at things in a negative light is just as easy as looking at things in a positive manner, you just have to take a different attitude.
I sometimes feel like I don't really fit into the accepted mould we are told leads to happiness but I know that I am happy with what I do so I don't feel pressured to change. I sometimes think that a lot of people that are unhappy are that way because they do what they feel they should do rather than what they would like to do.
Basically, if you are not happy and have got to the point where you don't even care to hide it, you need to reassess what makes you happy and what is wrong with your life. Do you feel that you should have achieved more, have a better job, a girlfriend? Pretty much everyone has an inflated opinion of their own talents and worth which can lead to resentment when that "potential" is not recognised for long periods of your life. Just bear in mind, peoples happiness is generally not linked to their earnings or wealth. We are always changing the goalposts for happiness as we achieve our goals that we think are an end point for our unhappiness.