I've been avoiding this manga because I don't want to be hurt. I can't say that I'm regretting reading this manga this late because the timing is just right to read and learnt from this story.
They are right, what is happiness? It's not right to say that Masumi is not happy because she did not end up with Futaba. Life is more than that. It's not about guy and girls, girls and girls, and guys and guys. Happiness is doing what you wanted. Happiness is not limited to what you can access. Happiness is not something you already thought about and already found. It can be found later in life and that is happiness.
Happiness is being free to do what you want. Love what you want. Cry when you want. Be angry. Have someone...
Happiness is different than other people's want. You can't tell someone what their happiness are.