So I've been with my boyfriend for about 7 months now and his family has met me long ago but only recently found out I was Catholic (or at least from a Catholic family...) and there wasn't really a good reaction to it... I know his family is Calvinist of Calvinistic but I don't know much else about it. Can anyone tell me why they tried to bounce around it and why such a negative aura came about after I'd mentioned I follow Catholocism??

I think it's just one those situations where they're afraid of the possibility of your religion rubbing off on him. If you can, try to find a way to show that you have no interest of trying to convert him or that you have nothing against their religion. This tends to be a pretty expected reaction when it comes to things like this, at least from my experience it is.

They probably think you're planning to ruin their way of life. Just do what Zhane says, and show them that you don't care what religion they follow, and that you won't force them to "just try Christianity out"

I may be able to help here some, I'm a wiccan and my significant other is a Catholic. Basically they're gonna judge you for a while, and its gonna be annoying, however they'll grow to accept you as long as you don't force your beliefs onto them/their children.