My 15 year old daughter was dating a lovely 16 year old JW boy while I was JW myself and I was happy about the relationship as they were chaperoned by myself or were in a group of other JWs and were planning to get married once they were both baptised and she was 16 which was only a matter of weeks away but no rush.
Even tho neither were baptised when the elders found out they still stepped in and threatened the lad with losing his goodstanding in the congregation and he would not be able to get baptised if he continued the relationship. The elders never even asked me how I felt but as a woman and raising my children alone my opinion would have been worth zilch anyway.
He chose the religion over my daughter and she was heartbroken subsequently refused to go to meetings and my relationship with her broke down. (We are fine again now)
I am still friends with her first love who is happily married to an elder's daughter and has 3 children he adores and he is a great dad........but he is JW. She had a lucky escape but we didn't see it at the time.
I do think if you try and separate them you will have the opposite effect and any argument against the religion is likely to fall on deaf ears if she is in love and may even come across as nagging or point scoring against him.
The boy should be able to articulate his intentions to you as her mother and if he is open to finding out the truth about his religion that might be your best course of action but if he choses your daughter he needs to understand he may lose everyone else in his life if he is disfellowshiped.
As you are not JW your daughter converting is not the end of the world and she may see that a minimum 8 hours a month door knocking and 3 meetings a week not be that big a scarifice to be with her love. A mum constantly down on her boyfriend's religion tho might be too much for her to take.
I was recruited in as an adult and back then I felt and believed forfeiting holidays like xmas etc and family was worth losing for the happiness I was promised but everything was a lie and fake, even their "love" was false.
Hopefully the relationship will fizzle out but if she converts, gets married and has children try to ensure she always has you. It will make her escape easier.
Feel free to PM me. X