Merry Crhistmas!
Sorry to hear how do you do. As you said, you're not the only one. Besides, you're not actually alone.
Also, Tweeter is not the real life. I can also tweet how lovely my family dinner is going, but in fact, if it really is THAT cool: What the hell am i doing tweeting it?
Nothing is perfect, not even our family, and it is quite understandable that they aren't that approachable.
Remember, you can't change the world, but YOU can change YOURSELF.
I'm in a similar situation with you actually. I'm kind of the black sheep (Even if you all thing it is a cliché feeling or something XD) and sometimes it gets to me.
But as you, i have the power to overcome sadness. YOU'RE HAPPY, you just forget you are. Your cat might be a lovely companion, but if you really want to feel connected, look for people that cares about you.
I'm not saying that your family doesn't care, neither to replace them. Family is unique and can't be replaced, but give other people the chance to know you.

If it isn't personal, what do you want for christmas?
Cheer up friend, blessings and happy holidays.