Hi Ashley,
This is probably the hardest question I have seen here. I will answer the best I can.
You are right to suspect your religion may be the reason for him not showing you to his family. He may come from a conservative/religious/traditional family that would want him to marry a girl from his culture and religion etc. But that doesn't mean he can't marry you. A Muslim man can marry a person of the Book (Jews, Christians, Catholics, etc.), however the understanding is that the kids would be Muslim (I take it you are OK with this since you are willing to even change your religion just to be with him). It is a little early to talk about kids though... It is also probable that he is not showing you to his family because he is shy since boyfriend/girlfriend relationship is not a part of Islam and his family would surely be upset at him. You being Catholic I am sure can understand, the modern way of boyfriend/girlfriend, and premarital relationships, is mostly sinful.
If your boyfriend is more religious then he'd be so happy if you converted I am sure, but you should not convert just for him or marriage. You should research the religion and give it close and careful consideration and only become Muslim if you truly believe in it. This is actually much easier than you may think, we have so many Christians/Catholics that become Muslim daily... and they do it simply because they know it is the truth and their is much proof to back this up. Even if you don't end up with him you should look into Islam further, if for nothing else, to know what Muslims are all about and to hopefully get rid of some of the silly misconceptions there are out there about us.
I hope this helps you a bit. I don't really know what to tell you...
I would recommend being open to him and asking him directly when he is in a good mood. I just hope he is not one of these men that is not serious in a relationship... I am so happy you wish to get married, that is the right thing to do. It is better to be married to go on and fall into very sinful actions...