Go to the KH with him and hold hands. It can be a not so subtle test of his intentions. A friend of mine dated a man one year ahead of us in high school. He was very bright and was accepted into medical school. Anthony was very dependent on his Italian Catholic family and my friend fit in perfectly. They attended Italian events together. She was not stupid but thick. Soon, Anthony had a Polish medical students as his other girlfriend. If he had a medical school event, the Polish one was the gf. If it were neighborhood Catholic, my friend attended. Both saw the other and hated each other. Sadly, they never connected as spurned women. They had so much in common. A boyfriend having his cake and eating it too. They were in anguish.
Growing up is partly deciding who you will be. If he is a Witness, he has no business having you as a gf. It is insulting to every devout sister. This trait would be understandable in a fifteen or sixteen year old boy. Teens need to experiment. Do you want to be part of an ongoing experiment at thirty?
The truly hot issue will be child custody. People get divorced with far less dividing them than a cult. I feel bad for you. The heart has its own rules. Implicit in your post and most replies is that it must be either one or the other. Maybe you need time to sit back and reflect. I want to act on things instantly, particularly things that my Witness background makes difficult. My mother committed child abuse by allowing me to go to KH and having Witness literature. Do you want your children dreaming of sports teams or heaven or Armageddon? It is a very steep price to impose on others. I respect an individual's right to choose but not to impose it. Maybe your bf is adamant that you will become a JW. This happened with a Jewish/Catholic couple I knew. Both assumed the other would convert to their religion out of love. Sadly, they were a great couple. Religion affects us more than we understand. They broke up. Each married someone of their own faith.
I grew up where marrying an outsider was romantic. Jewish/Catholic marriages were heralded. The fact is tremendous tension exists. Some people can beat it. Not many.
Let the process wind its course. You are seriously considering the future. He could use your support as a friend or lover. Of course, lover doesn't exist for Witnesses. Maybe the two of you can beat the odds. It sounds as though your tolerance is waning. JW seems to be part of his very being,not clothing for him. What does your gut say? Listen to your self and not anyone else.