Princess
There has been some damn good advice on this thread, so please give it all a good read! This situation has also come up many times before so please have a look at some past posts too.
When I was a staunch Jehovah's Witness about six or seven years ago I fell in love with a non-JW and her name was Gill. It was very painful experience for me to fall for someone "in the world", I was very inexperienced and so I was very bewildered about it all. But I had to do what was "right", and so I never took the relationship any further than a close friendship. She was a very very good friend, and I had this dumb fantasy that she might come in "the truth" one day, so that I could go out with her properly, but of course it never happened.
I look back now and think what an idiot I was for letting her go, knowing what I know now – I’m filling up with tears just thinking about it. She of course eventually found a guy that didn't have any baggage, and when she told me about him, I pretended that I was so happy for her, when instead I just wanted to die. She is now blissfully happy somewhere down in the southeast of England, having a darned better life than I am having right now.
So my advice is, give the guy a plain, stark choice; and try and be firm about it: it’s you, or “the Witnesses”. And for god’s sake don’t ever become a Jehovah’s Witness just to make him happy – and don’t fool yourself that it could be just a “temporary” thing just to keep him happy. He’ll be a damn fool for letting you go, just like I was all those years ago for letting that girl go. I know it’s easier said than done, but if he truly loves you then he will make the right decision. Perhaps if I were given such an ultimatum I would have got out of this darned religion a bit sooner!
Best of luck