Happiness is not something that others can take from you. It's something that you would have to throw away on your own.
There will be times when things don't turn out the way you want them to. Your best friend at work may turn out to be a power-hungry corporate animal that backstabs you at every opportunity. The promotion you worked so hard for may go to someone else. Your partner might decide to leave me, a day before we are due to go for a vacation together. You may lose most of your savings in a market crash.
These are things that can happen to the most loving, compassionate, careful and reasonable person. But after the initial pain and shock, the decision whether or not to let yourself languish in despair is entirely up to you. You can allow misfortune to form the bulk of your life, or you can choose to leave what's past in the past, and move on.
One's friendly and caring behavior towards others should not be motivated by the thought of equally kind and affectionate responses. You understand yourself best, and regardless of how reasonably and responsibly you live your life, there will be people who won't see your point of view or share your motivations.
People have the right to act in any way they see fit. I don't have the right to judge whether their behavior is acceptable or not. They have to bear the responsibility for their own actions, and so do you. By feeling sorry for yourself, you are simply continuing the work for them, long after they have dealt their blow. You have to decide that, as far as possible, you will not allow these people to disturb your mind.
There are many things for which you can be grateful. There are yet unexplored experiences in which you can find enrichment and meaning. There are yet others who will like you for who you are, and in spite of who you are. If you spend my time being resentful and miserable, you are denying yourself the satisfaction of enjoying what this life has to offer.
There are enough unhappy people in this world who punish themselves and others constantly in a bid to find redress and compensation. But there is no satisfaction in retaliation and revenge. It's a waste of time and spirit.
"To be happy we must not be too concerned with others."
Albert Camus