it is possible that he thinks your relationship is not that deep

which is worth to see his parents yet. You know,when a guy bring his girlfriend to see his parents, that's a very big thing. So I think your feeling and his feeling has some distance here. You 'd better re-evaluate your relationship with him and either you slow down for him or let him catch you up. Or it will have some problems or misunderstanding again soon and it just simply does not work it out.