IF, and this is a big IF, as he get's older and can investigate the JW religion for himself, you may be able to open his eyes to the reality of what the JW religion is. Many young people raised in the JW religion have never seen the 'other side' so to speak. If he is already willing to involve himself with a 'wordly' (non-JW) girl, it shows that perhaps he already isn't TOO concerned with the JW rules. Although hormones in a teenager tend to over-ride anything else, and I hope that once the infatuation wears off he doesn't get a 'guilty' conscience and dump you. It's happened MANY times before. Trust me, he's getting or willget SERIOUS grief from his parents about you, and the elders in the JW church if/when they become aware of it.
IF you can open his eyes to the religion, you MUST replace the brainwashing that he has been raised up in with something else. Otherwise he will continue to beleive the JW teachings even if he were to be kicked out (disfellowshiped). Many disfellowwhipped people will go years away from the JW religion, yet still be mired in those beliefs - if they don't learn the 'truth' about the 'truth'.
Best of luck to you!