Happiness is all that we constantly seek, am I right? I'm completely sure you'll agree with me on this one, because what else do we seek?
Even if we seek any other thing as making friends, being wealthy or any other desire, we do so to achieve happiness, but we sometimes fail at defining happiness.
Happiness is different for each and everyone, so you should define it for yourself, but what is common at all of us, is that happiness mainly consists of gratitude, so as a matter of fact, not one is grateful and not happy, and the exact opposite is right.
Marcus Tullius Cicero said: "Gratitude is not only the greatest of all virtues but the parent of all other"
Pointing to that any other blessing also needs gratitude to be a blessing, and without gratitude, you really have nothing in this life.
So, instead of constantly seeking what you miss in life, stop for a while to count all of your blessings, and be thankful for their existence, be grateful for all the things you have in life, for everything you have achieved in life, and you'll definitely achieve happiness.
Also I highly recommend that you start having a gratitude's journal, to write all of your blessings, achievement, everything you have and you're grateful and thankful for having, so even when you feel down, you'll find so many things written by your own hands to cheer you up, and as a personal experience, it never failed to cheer me up.
So that was all for today, I wish you a happy, grateful, and thankful life, and in short words, a happy one :)