I thought that a marriage is not just a religous ceremony and a civil union. Legally, its something different, right?
I'm having a bit of difficulty answering your question, because 'Civil Union' has a specific legal meaning here since we legalised same-sex marriage, i.e. a same-sex marriage is called a Civil Union here (notice the capital letters).
But my original post was distinguishing between the religious ceremony you go through to satisfy your religion's marriage sacrament, and the paperwork you have to sign to satisfy the state that you are married, i.e. the 'civil union' bit of your marriage (notice the small letters). You can do the latter without the former, but you can't do the former without the latter (well, not if you want to be treated as legally married).
So to go back to your original question:
So if I got married then I'd have to get a civil union too?
You don't have to go through two ceremonies, no. But if you're going for a religious ceremony you have to satisfy both your religion's requirements, and the state's.
Edited by JavaMan, : Changed 'the government' to 'we'
'I can't even fit all my wife's clothes into a suitcase for travelling. So you want me to believe we're going to put all of the planets and stars and everything into a sandwich bag?' - q3psycho on the Big Bang