First:
Even if you have been married forever, you are still YOU. You know the old way of saying your spouse is "my better half"? It's not true. When that person dies and you are alone after so many years of being together, you are still YOU. For a long time it feels like half of your heart is ripped out - it just hurts so bad - but you are still the same person you were before. You have learned a lot, you have experienced a lot, and - if you are one of the lucky ones - you loved a lot. But you are still you with the same personality, the same values, the same heart. You didn't lose your other half because you are still whole. You just have to learn how to adapt, to live life on your own terms. Just like before you got married. It is not easy, but you can do it. I know this from experience. Let yourself heal and remember who YOU are.
Second:
You raise your children to the best of your abilities. You love them, you teach them, you support them, you give them all they need until they become adults. After that point you cannot help them any more. They will be the people they want to be no matter what YOU think they should be. And it is no reflection on you (unless you did something really terrible to them as children). Sometimes they just CHOOSE to be stupid! And you can't fix that...
Third:
You never know when you will lose someone close to you. You have to appreciate them for the NOW, not for some future time. Spend time with the ones you love - family, friends, anyone that has been in your heart. If something happens to them the memories will be all you have. Make them good memories, give back to them what they have given to you. Love, friendship, compassion, laughter, support - it all matters so much when they are gone. That is all you really have of anyone anyway, the only thing that is permanent is the memory of that person. Take the time now. It will work for them when YOU are gone as well.
Fourth:
I am stealing this from my mother (who heard it from my grandmother I am sure).
"If you don't have something nice to say, don't say anything at all."
If there is someone you really cannot tolerate, just stay away from them (and do not talk about them behind their back). Unnecessary drama is not pretty. It is so amazing that the people who profess to hate drama the most are usually the ones that create it and perpetuate it. It makes you look small and petty. Just don't.
Life is too short. Stay away from the drama kings/queens, the hypocrites, and those that choose making other people's lives miserable as their chosen role in life.
And make sure that you are not and never become one of these happiness vacuums.
Again, life is just too short....