You've received a ton of responses and I haven't had the time to read them all yet.
I'm a faded witness but my wife and family are currently active.
My 2 cents:
If he leaves the religion for you then he'll probably return to it one day. The witnesses have a strong psychological attachment to their religion. Guessing by your college major you probably figured that out already. Proof of that attachment is the fact that you've not been introduced to everyone in his life and that he is purportedly still a witness while doing many many things that go against his religious creeds. Living 2 lives must cause a fair amount of stress. In his mind he's playing both worlds. That does not mean his love for you isn't real - from how you described him it probably is very real.
The caution is that at some point later in life something may happen, be it old age, severe medical trauma, having childen or whatever he is probably going to return to the witnesses. If he becomes an active witness in good standing then unfortunately your relationship will change.
You need help him realize that the witness religion isn't "the truth" and that being a witness isn't an automatic ticket into a new system. Until you (or someone else) does that you will always run the risk of him returning.
I wish you the best of luck. Sounds like you know what you want in life and are going for it. Great job.