Should I be concerned over the fact that I've been ...

Hi,
Yes you should be concerned.... He is, most probably hiding you from his family..... or telling them you are muslim too.....  It's a clear sign that he won't go any step further in your relations....  No offence please.
Best regards,

The issue of different religions can be quite problematic. It is an issue that you should be very concerned about, and if he is serious about the relationship, then he should try and resolve this matter before the both of you decide to continue. Have the two of you sought professional help from a social worker, (or other professional) member of the clergy, or friends and that are in a similar situation? Has the issue of conversion been discussed? You need to resolve this matter as soon as possible.

Hmm, that's a tough one.  I would be concerned to some extent, especially since you all have been together for three years now.  I mean after three years, he is should or is likely thinking about some commitment to you and it seems odd that he would not introduce you to his family.  I have heard of this before as I have a friend who is Korean and is not allowed to marry anyone who is not Korean.  Sometimes, it is a religious thing and sometimes it has to do with culture.  Why not tell him how you are feeling as I am sure you are comfortable with him by now.  Has he given you any good reason why you have not met his family?  Has he met yours?