This is a scenario I've never heard of before! I misinterpreted the title of the thread as meaning 'dear best friend', for some reason... now that I know it's your boyfriend you refer to, my response is completely different!
I have friends who buy fakes (one or two, most of my friends don't buy designer goods at all and wouldn't be interested in a fake or in an authentic piece) and I've tried to explain why it's not a good idea. However, after they either just shrug it off or get defensive, I don't bother mentioning it again.
If it were my partner, I'd definitely have something to say! I don't know about you, but I wouldn't want to be seen out and about on a regular basis with my genuine LV if my partner was carrying a fake. I don't know if this is wrong, but I really would feel like it was cheapening my entire look. That might sound superficial, but it's true - I don't think I'd carry my LV at all when with him.
Just tell him it's a waste of money. Tell him you don't expect him to buy you LV, and that if he really wants some of his own, he should invest in the real deal. He MUST know there's a huge difference, from seeing your pieces!