Trying,
Welcome to the forum. I'm glad to see that you've recognized current problems and can foresee additional problems over the long term. Too bad you didn't ask these questions earlier, before investing 1.5 years in this relationship.
From your initial post, I determine that you don't really know much about JWs or the Watchtower organization. This group is not equivalent to any other religion but is highly controlled and very dictatorial, some say CULT. Ideas and beliefs presented, are not items that members may wish to adopt, but are required beliefs that must be adopted by all JWs, without question or consideration.
Member's minds are conditioned that the WT is God's true organization on earth and that JWs are God's special, chosen people, believing that they are the only group that will survive Armagedon, contrary to what they may tell a non-believer to their face.
You'll probably recognize that it's easiest to teach a person as a child and that what is taught to a child will remain with them and is the hardest to change. Since your BF was raised as a JW, what he was then taught will always be with him.
JW's SHUNNING family members because they no longer practice being a JW is a requirement dictated by the Watchtower for every JW. It is not an option and something only a few extreme JW's do on their own.
By 'pretending' that his son is not living unmarried, with a non believing woman, is a means of the Father not having to shun his son as he doesn't 'technically' have proof of his living arrangement. Once the living arrangement has been confirmed, he will then be required to shun his son and you.
Your boyfriend is fooling himself into thinking that he can live whatever way he wants and still maintain a healthy relationship with his Father. Acceptance by his Father is not your BF's decision otherwise, to be accepted, he must be a fully practicing JW, following every requirement as defined by the WT. Anything less will not be enough and will likely result in shunning by his Father if not his entire JW family.
For YOU to be accepted by his JW Family, you too must be a fully dedicated and practicing JW. Do you have any idea of what is involved? Do you know how many requirements are contradictory to the bible and how much unquestioning allegience must be shown to the Watchtower organization? If you didn't wish to become a JW, would your BF hold it against you for any breakdown in his relationship with his parents? Are you prepared for that?
Do you realize that if you and he had children, if your child was ever injured, as a JW, you would be required to fight against administering a blood transfusion even when the Doctor's determine that this treatment is required to save your child's life?
I have seen many occasions where people raised as JWs, even after not being active members for many years, hold onto the notion that JWs are the 'True' religion and will suddenly return to it. Often the catalyst will be a major event in their life such as birth of a child, loss of a loved one, illness or even marriage. Quite often, they will become extreme in their devotion and place many unreasonable conditions on the relationship with their partner.
For your BF to become a partner that you can rely upon over the long term, he must first come to terms with recognizing that the Watchtower and the JW religion is not the 'Truth' or God's chosen organization. Not practicing and promising he'll never return to being a JW is not enough. Until he is ready to look into this issue, he will likely defend the religion, organization and current teachings, even if he's not practicing. Unless he comes to terms with reality, this issue will always be in his background and mind and can surface at any time, current or future.
JWs are conditioned to believe that God comes first before their marriage partner. Since the WT holds itself as God's true and only organization, they place themselves as God's spokesman on earth. Whatever they say is coming from God will come first and your relationship with him will always be secondary. Since the WT promotes that men are the head of household and women are 'the weaker vessel', you will likely never be an equal partner.
Although no one can predict that your relationship will not work out, unless your BF is ready to deal with and acknowledge the 'falseness' of the organization and religion and knowingly put it behind him, any long term relationship with you will be made more difficult and trying for both of you and may be doomed from the start. Unfortunately, dealing with and accepting the falseness of the religion often has a high cost, usually a breakdown in the relationship with believing family members.
Bluntness of comments made on this forum, is an expression of concern for you as no one desires to see you hurt or involved with a relationship made difficult if not impossible due to religious programing.
I believe everyone here wishes you and your BF well and that you and he can work through this in an informed manner.
You may want to read through the 'Best Of Topics' section of this forum as situations similar to yours have been previously addressed. Ask any other questions you wish.