You've upset him
Now we're going to do a bit of stereotyping here, sorry, but we think it's kind of true. On the whole us girls are pretty good at ignoring someone when they've annoyed us.
Men are, on the whole, more likely to say something whereas we're more inclined to do the whole passive aggressive trick.
Not all boys are the same though, so have a think, if your boyfriend is ignoring you have you done something to upset him? Have you said something a bit insensitive? Or have you been ignoring him?!
He might just be giving you a taste of your own medicine.