I would absolutely NOT recommend marrying this person.
I know that might be painful to consider. Maybe too painful.
I would try to think of your unborn children. You are playing for very high stakes here. Will you raise them as witnesses? What happens if they have an accident that includes major blood loss? Will you let them die rather than allow them to recieve the lifesaving but forbidden treatment?
A person either believes the JW is the "right" religion or they don't or not sure. If your bf believes it is the one true religion, then you can bet your ass that once you have kids, he will want to raise them in the religion.
You will be an unbelieving mate. You will be second wife to his first wife, the Watchtower. All major decisions about your life, the children's lives will have the organization giving the final say. Your husband will follow their dictates, and because they are from God, they will be non-negotiable.
Sorry.
The pain of passing on this is more imminent and acute... but if you take the long view of your life, that pain will likely register as a mere blip when compared to the pain you and your children could experience as a result of making this choice.
Choose carefully Mommy, your babies are counting on you.