I try, I really try- to see all sides of a thing. You have invested all those years, you love him. He finally told his parents about you.
So, if what you have read from sincere people doesn't get you to break up with your JW boyfriend, perhaps you can proceed with a new viewpoint. Maybe the information here will open your eyes.
JW men are the head of their household. He thinks he will be the boss, no room for compromises on that. Even if you don't see that so much in him, his religion teaches him that. He will raise his children in that religion, it will be very important for him not to compromise there- no exposing them to both sides of the issues and letting them freely decide about birthdays, holidays, Mother's Day, sports, entertainment, yadda yadda.
If you think it will all work out, then try to make it all work out now. Be a bigger part of his life, no matter what his family and fellow JW's say. Tell him you aren't interested in becoming a JW, but would love to be on his arm at the Kingdom Hall to meet these people and see what the meeting is all about. See how well that goes. Surely, he would want to have the woman he will marry see that part of his life and surely two people dating for 5 years should be able to sit together and hold hands in "church" and meet people. You can let him a little off the hook and tell him he doesn't have to say to JW's that you two are "engaged" but have been dating for "awhile since High School."
Let us know how well that goes for you. From that point, maybe you could double-date with some JW's. And certainly, you will want to meet and spend time with his family.
I think the way all that goes down will help you to know what you need to do about this relationship. Good luck.
