I believe you can make the choice to be happy. Sometimes it means to just simply act as if you are happy. What I really mean is that you can choose to focus on the good and find joy in it, to practice positive mind habits such as responding to situations mindfully and in ways that bring you the most inner peace. The first step is to actually live mindfully. Most people don't even know they aren't aware or awake. You can only be happy if you choose to be so. That doesn't mean you won't feel sad or angry or hurt, but you can choose how you respond to and embrace those feelings.
Well, put it this way. If you choose not to be happy, you will be unhappy. :) So why not choose to be happy? And then do your best to do the things that will bring true happiness, true inner peace and joy.