My mom is a devout Catholic and dated a Jewish man for over 4 years in the '60s. She said they decided to go their separate ways because they just couldn't bridge the divide, so the speak. I don't know the exact reason, but I suspect it's not necessarily because he was Jewish, but that he was pretty much agnostic. If he was observant, maybe it would be another story. She said his family was very kind to her, though, and she went to his wedding. They still keep in touch once in a while, he's married with a few kids but not in the best of health right now.