How much is the religion important in a couple?

I think some cohabitation is possible (in the States Protestants and Catholics coexist although they don't so well in other countries) but if your beliefs are too different (Pagans and Catholics, for example) it will eventually cause problems. Even though a lot of the core values are the same - be kind to humans and animals so that they will be kind to you, don't do anything to intentionally hurt another, those kinds of ideas - the methods for teaching and practicing those values are vastly different and that will cause conflict. I am a Pagan although not practicing and my ex-idiot was raised Catholic. He and his younger sister had abandoned that faith but their parents and grandparents, aunts and uncles, etc still followed it closely so even in that situation I was a bit uncomfortable. Even though I knew his parents had accepted his and his sister's decisions, there was a lurking feeling that they still thought we were all condemned for not believing. So like religions in the partnership isn't the only thing that is important. Their family's beliefs, your family's beliefs, all will affect the situation.

Yes, I think cohabitation is possible between people of different faiths. It's just a matter of communication and coming to an agreement as to what one expects from the other in terms of understanding one another's faith. I can vouch for it because I have family members that have made it work. ^^,

I think it's perfectly possible. I see it happen all the time. My mother is Methodist and is with a Catholic. I used to be Methodist and my fiance is agnostic, sort of. My grandfather used to be atheist (possibly agnostic, who knows?) and my grandmother is the most devout Methodist you'll ever meet. Yet, all these relationships have worked. Then again, my family very much feels that you can believe whatever you want to believe and you have that freedom, but don't impose it on others, not even your spouse or your family. Not even your children. We feel very strongly that people have the right to their own opinions and to form their own beliefs because that's what makes them who THEY are. ^_^