Most Helpful Guy
Call your boyfriend, tell him exactly what you wrote here about what happened that day, that you took pity on the ex because he was all alone on xmas, and that you might have been naive to welcome him at your house but that you were firm and just confirmed him it was over.
At the moment your boyfriend must feel very insecure about your feelings at least, or betrayed at worst, and ignoring him will only increase the damage.
You should have thought a bit more before inviting the ex, so now you have to solve the situation, because it won't get solved by itself.
If you tell him that nothing happened except you rejecting your ex, and if he really is into you, he will understand.
Good luck :)