You're in for a difficult ride if you stick with him. You've had a short relationship, so I suspect that most here will advise you to run as fast as you can, but only you can make the decision regarding how much you want to try and potentially sacrifice knowing that there's a strong chance that this will end in heartbreak.
My advice would be to have a serious conversation with him to gauge his motivations and level of indoctrination. See if you can get him to review the content of jwfacts.com, the book Crisis of Conscience, or the book Combatting Cult Mind Control. If he refuses this is evidence that the JW indoctrination is still very strong. If he agrees, there's a good chance that he'll "wake up" and realize the extent of his indoctrination and the systematic deception that he has been subjected to.
If he's simply getting reinstated so that he can be around his family, then no big deal...if its because he believes in the cult doctrine then your relationship probably has an expiration date. The elders are often very snoopy and there's a fair chance they'll discover your relationship and he will not be reinstated if he's living with you while unwed. Between this possibility and the guilt he'll feel from meetings and the indoctrination about "worldly" people (which includes you) there is a fair chance that he'll end the relationship as he begins to rejoin the cult.
I hope things work out and I hope you're able to free him from his indoctrination. If he's saying that he's only getting reinstated to please his mother then I think you have a chance. Unfortunately getting reinstated (or making the effort to do so) can have some powerful psychological effects that may cause him to embrace the cult on a greater level. The social pressure he'll be subjected to will be strong as well. Your best chance is to try to free him from indoctrination before his involvement with the cult grows. It would be a good idea for you to read Combating Cult Mind Control regardless of whether he does. This will help you understand the indoctrination that he's been subjected to and it will give you a better chance of freeing him from it.
All that said, no one would blame you for simply deciding that this is all too much and moving on. This is a HUGE undertaking and a HUGE risk to your emotional and mental well-being.
Good luck! I'm wishing you all the best in this, whatever path you choose.
