When does religion become an issue...

I've been in my relationship for over a year and we are pretty serious about each other. We talked about potentially getting married eventually if we were both ready to make that kind of commitment to each other. We were talking yesterday about things and realized how much we actually differ on the big issues, like religion and politics and how we would raise our kids eventually. It didn't go very well. He's catholic and so is his family and I am Buddhist. Our beliefs and opinions differ greatly and it clashes with wedding ceremony ideas and how we would raise our children...I know it's not for a long time, but if we were to make that kind of commitment, I'm afraid this would be a really big issue and ruin things. Does anyone have some kind of advice?