A long time ago I learned two nifty ways to express the idea of "I'm leaving" in Spanish:
Tengo que irme (or Me tengo que ir) and Me voy.
The problem was I had no idea what the difference was between the two, so I asked a couple of my amigos (one from Argentina and one one from Colombia), and this is what I learned...
You know how you're at dinner or a party having a good time, and you realize it's time to go? So you start with "I've gotta get going".
Thirty minutes later, you say it one more time.
15 minutes after that, you say "OK, I'm leaving" and finally walk out the door.
Well, in Spanish to express the idea of "I've got to get going", you say "Tengo que irme". Maybe you get up and leave, maybe you don't.
When you finally reach the point where you're actually leaving, you wave goodbye, dole out a few besos and abrazos, say "Me voy", and head on out the door.
Well, there you have it. Y ahora, ¡me voy!